I have Serana as a follower and right now she is only carrying about 25 lbs (or whatever the units are) of stuff i gave her and I can't give her anything else. Also if I take the stuff away it still won't let me give her anything, it says she's at her limit. I don't know what to do it used to work fine, any ideas on how to fix it? Also I'm on the xbox.

Her armor plus scads of hoods (a small error in the script that controls her wearing her hood outdoors can give her large quantities of them) must be weighing her down.

To fix:

Give her something to make her put on her hidden hoods, and make sure she's wearing her Vampire Royal Armor. The best bet would be a weapon -- try dropping one on the ground and having her pick it up. Once she has it, take it away -- with luck, and if my hunch is right, she'll put on her hood even if indoors.

Now you need to make her follow you and take her somewhere where you'll pass repeatedly between locations without going outside -- best bet would be Dwarven ruins leading to Blackreach, or withinn Blackreach going between the Tower of Mzark and the main underground area.

Now, you'll need to get her to wear her hood while transitioning between areas (in most cases, riding elevators). If she won't take weapons, try lighter ones -- the Ghostblade found in Anslivund weights one unit; iron daggers are the next lightest at two. Give it and take it back, and she should equip her hood.

Do that back and forth until she stops putting her hood on -- you're "tricking" her script into thinking she's going indoors so she needs to take her hood off.

It's tedious, yes, but it should work.

And it will take a while -- her armor weights 11 units together; her hood weighs one. Followers can carry 300 units total. If she's being overburdened by one-weight hoods...

I just want to make sure i understand you correctly before I do this a hundred times only to find I was doing it wrong. So I am at the elevator between blackreach and Mzark. She is wearing her vampire hood and royal armor, and I just go back and forth between the two locations until it's fixed? Am I supposed to do the whole give her the weapon then take it back each time or can I just go back and forth?

On a side note I can't drop something and order her to pick it up, I've never had the option to give her a command, I don't know if that's normal (I've finished the Dawnguard main quest if that makes a difference.) This isn't important for me because I don't use it anyway, but if it's necessary to fix the problem I'll just have to live with it the way it is.

never mind it's working! you're right this is going to take a while. Thank you so much.

Give her a command by holding down the activate button while hovering the cursor over her.

And thank you.

I had this happen before, too -- thankfully, I'm on PC, so I just used the console to remove the excess hoods.

Now I've just got to figure out where her script goes wrong...

And FYI: she won't put on her hood if she's not wearing her Royal Armor, so if you'd like to stop this from happening again, give her some light armor that's Elven quality or better to wear instead.