So your previewing textures in game by saving to a custom folder, K. Here's a check list for you to run through:
Make sure the files are named correctly. Bicep & tricep textures should be called:
l_biceps.tga
r_biceps.tga
l_triceps.tga
r_triceps.tga
They need to be .TGA files saved without RLE compression & the origin set to bottom left.
Make sure they're 128x128, RGB colour & have an alpha channel (transparency) - you'll need the alpha even if your not using it.
A correctly saved texture file's size is 65k