That particular error is caused when the mod author uses a different version of the master file (Morrowind.esm in this case). It's nothing to worry about, but there are two ways to fix it. The first will re-date your mod, which isn't always a good thing. All you have to do is open the mod in the CS, which, since you're using Steam, you probably don't have.
The second way is to use Wryemash to update the mod to the version of the master file(s) you have.
http://www.gamesas.com/topic/1331996-yacobys-wrye-mash-fork/
Thanks, it seems so simple, if only I wasn't a PC noob and I could understand what all that jargon meant.
I know my free help cards are running out, but I've come across another problem while trying to get some new playable heads in the game. I put all the files in their folders, check Wryemash, it's all green and says it's good to go, but when I start a new game and go to choose my character, as soon as I get to where the new heads should appear in the window I get a message, but due to the head in the way I can't read it. It goes along the lines of:
'--ad access files from
(Some file name like Emma/nif8)
(The file name again and something before it I can't read)
Would you lke to continue running executable?
Yes No'
It doesn't matter which I pick Morrowind turns off anyway. This is the second head replacer mod I've tried and it's been the same problem. Her (Emma's) website didn't say anything about needing MGE or anything, and neither did the read me, so I'm all blank.
I know this is vague, and probably not helpful, but as always, any words of wisdom would be much appreciated.