Right heres what i tried to do. I was makeing some armor and i thought it would be cool if the NPCs armor had weapons on it so i had an idea of how i wanted it to look. so i opened up blender and exported the armor i wanted in. It had the skeleton and eveything so i loaded up the weapon i wanted on and put that in the posistion i wanted. So once all that was done i exported it as nilf (well duh) opened up nilf skope and assinged the custom textures i had made (they had normal maps and glow maps assinged as well) set it up so it all looked great in nilf skope just how i wanted it. So i open up the set create the armor and assing the armor biped model and the world model. So far so good i also told in were the armor was being euiped so upper bod, lower body,feet and hands press ok. Place it in the world. And save i open up oblivion go to the armor pick it up euip it and my whole body minus my head dissapers. now the only thing diffent is that thier are weapons on this mesh.

Can any body help me out here please im desprate.

just as a side note i had the weapon as a indviual weapon euiped it and it worked fine and that is all i have done nothing else

Sounds like you didn't export the textures properly

could you elabrobate please

Well if you were invisible that probably means that there were no textures added to the model

Go back to the basics of modelling and learn UV mapping over again

Some silly things that caught me out when I did this (and made it go invisible) - It always when your rushing to finish something that you make the stupidest mistakes......

Not setting the armour for both male/female bodys and trying to use the wrong one (Duh)

Try assigning the textures using TR (Texture Replacer tool look on google or nexus) this makes it dead simple and you can then eliminate the paths as the cause of the problem.

Do the armour show up correctly in the CS? Or is it purple? (if you add it to the inventory of an NPC do they dissapear too?)

This is normally caused by being assigned to the wrong slots. Try unchecking the Feet/hands slot or maybe you missed something amulet/tail slot for extra bits?

i dont think i made my self clear i have not made a custom mesh what i have done is taken a existing armor model (dark brotherhood armor) in blender i have imported weapon models (glass dagger) and postioned the dagger in the place that i wanted (the chest) it is touching i then exported as a nif then in nif skope i have assined retextured versions of thier orginal textures saved that and put that as the model in CS

and my promblem is that its invisble it dissapers in game can anbody see anything (no pun inteded) i might have done wrong just to clarfiy the textures are working they do have normal maps and they show up fine in nif skope

The file structure of a NIF file is very easy to mess up and it will still work in NifSkope. Importing into a modeling app and exporting is known to corrupt things when the im-/export settings aren't 100% right.
Disappearing meshes ingame doesn't necessarily mean there's something wrong with the textures (missing normalmaps), it's even more likely the file structure got messed up beyond what the game engine will tolerate.

The OP said he imported an existing armor and added a few weapons. It's hard to mess up the texture settings of body parts in existing armors, so telling him "that probably means that there were no textures added to the model" and "Go back to the basics of modelling and learn UV mapping over again" isn't really helping (the UV maps are already there and working to begin with), sounds downright rude and offensive, and only creates the impression of not having read the OP's posts completely.
What is easy to mess up in this process though is getting the weapons to act as parts of the armor. Weapons are not "rigged" like armor but mounted to the weapon node by its BSX flags. They need rigging (weight painting) to the armature of the armor or they won't stay attached to it.
But yet more likely somewhere in this process the internal structure of the resulting NIF got corrupted, like the top node is no longer "Scene Root" (the top node of the weapon file was the name of its type, e.g. "long sword" etc.) or there are objects not children of "Scene Root" but on the same level or something. These are all things the game engine won't tolerate while NifSkope couldn't care less.

I suggest show us some screenshots of the NIF tree or even upload the corrupted file somewhere for us to download and have a look.

thank you for that and here is a picture of the mod in nif skope with the roots expanded for each part for you to have alook at i tried to get the image quality high as possible

http://s825.photobucket.com/albums/zz175/michael10101hithier/?action=view¤t=modpic.jpg

The daggers are not weighted to the skeleton. If you don't do that theyt will collapse to a point at the root as soon as any animation plays, and that's all the time. Which means they disappear as soon as they're in the game.

What Drake the Dragon accurately described applies to weapons that are dynamically added to the figure when equipped, and are NOT part of the armor nif. It's possible to add two new attachment points for weapons to the skeleton (not the armor) to hold those daggers, but then they'd be independent of the armor.

If you want the weapons to be part of the armor, not separately equipped items, then they must have every vertex weighted to a bone of the skeleton. You can't do that in NifSkope, as far as I know, you'd need to use Blender to assign bone weights. It's actually really simple for a rigid object like these, as each vertex gets a weight of 1 for the selected bone (paint it plain red).

Note that they cease to be usable weapons when they're part of the armor. You can't use them as daggers any more.

Yes, what I see in the screenshot is what I expected... another Scene Root inside Scene Root, the daggers as NiNodes with the actual NiTriStrips/Shapes inside of them... these are all things the game engine won't like and thus the NIF file structure is corrupted.

Now, it's not quite easy to explain but not really very complicated to get it done right either.

You need to make sure there's only 1 armature in the whole .blend file, the one of the armor.
The weapon meshes and scabbards you imported need to be "parented" to this armature.
Select both, a weapon/scabbard mesh and the armature, and go to "Object => Make Parent => Parent To Armature => Don't Create Groups" (or something like that) and you'll have parented one of those meshes to the armature. Repeat for the others. That should hopefully get us rid of the multiple Scene Root issue already.

As for rigging those unrigged meshes to the skeleton, well, let's see... those 2 glass daggers could certainly be rigged to one of the spine bones, but I don't know how they will react (and clip) when the upperbody is bending up or down as different sections of the chest of this armor are weighted differently to more than 1 of those bones. Maybe with copying the bone weights from the armor mesh in this case you could even achieve yet better results. (Granted, scabbards and daggers bending when you bend isn't really realistic, but it'd require a little more serious conception to make it look right when only rigged to 1 bone without clipping in this position.) For copying bone weights select the dagger/scabbard mesh and delete all its Vertex Groups. Then select the dagger/scabbard together with the mesh you want to copy from (the chest of the armor) and go to "Objects => Scripts => Copy Bone Weight". Quality 3 or 4 should be alright and hopefully the meshes aren't too complex and it won't take too much time computing the resulting weights.

Is this another dagger on the wrist I see there? This one might work rigged to the "hand" bone or the lower arm perhaps. In this case bone weight copy could only mess up the rigging as it would connect it to all fingers likewise etc.

If you want to go the "rigging to 1 bone" route though, it's yet easier to just select the whole thing in Edit Mode ("A"-key) and "Assign" the vertices with a weight of "1.00" to the Vertex Group of the 1 bone you chose.
If there are no Vertex Groups already, just create a new one and name it accordingly "Bip01 ..." matching the name of the chosen bone. Maybe in this case "Don't Create Groups" while parenting wasn't the best choice either.

You can even test the bending and rigging of everything in Blender by selecting the armature and going into Pose Mode. As long as you only right-click instead of left-clicking any rotations ("R"-key) you do to the bones will not alter the armature but the bones will always return to their initial states.

edit: Uh, almost forgot, not all imported armatures can be posed of course. If they're not in a hierarchical structure already (bones as children/parents of other bones), this will not work. In such cases I always import a clean armature (e.g. from skeletonbeast.nif) with the "Skeleton Only (Parent Selected)" option and then afterwards import the actual armor/whatever mesh with the option "Geometry Only (Parent To Selected Armature)" while of course having the previously imported armature highlighted.

Hopefully that got us rid of all the issues in the NIF file structure after export.