Did you change your textures here?
http://www.project1999.org/forums/showthread.php?t=2482
If so, did you move all your .s3d files into a seperate folder? If so you'll need to move some of those back into the EQ folder, as there was only about 383 .srd files for the new textures, but about 1000 .s3d files you backed up.
The easiest way to do this, is to copy all the .s3d files into the EQ folder from your backup folder, but when it asks if you want to overwrite just click "do this for next x files" and choose don't move. That way you copy over everything else, and still retain your new texture files.
If this isn't the case, you will need to reinstall. That's the easiest way to ensure you have all the necessary files.