actualy things have changed a bit in version 5.2 of the launcher, so a little better way of phraseing what you have to do to fix the likely cause of your problem is (assumeing you're useing version 5.2 of the launcher)
open the launcher,
go to the "features" tab,
select 'Graphics' type (it'll probly already be there),
look for "Enable jpg,tga textures",
make sure you have a check in it's box,
hit the apply button, just to be safe,
hit the run button, and come back here if you still have problems.
note to fellow developers: we realy should probly just turn that on now, I've never heard any problem comeing from it.