Since you just posted about TGAs, I'm assuming that youre using them
if so, it's because the TGA is compressed. EQ only supports uncompressed Tgas.
Take just a couple of seconds to search and you'd come up with something very useful...
http://www.eq2interface.com/forums/showthread.php?t=605
I mean heck, its even named "Image in tga format showing up in UIBuilder but not in game ?"