You get this problem if there is an error in the .thm file, which, I believe is an issue relating to the fact there are two theme switchers around...LSTS, and LSCP...one needs a .thm file to locate the theme's step.rc and the other doesn't.
Anyway...I use LSCP and a few of my OTS themes caused probs with some people because they were using LSTS....but the 'step.rc' line in the .thm file was 'altered' and the step could not load, therefore, no modules loaded.

Who said OTS was idiot-proof?...LOL