I have to agree with Jatx2wne!!!! Rom Manager can be hit and miss sometimes as far as installing themes. I used to install my first 2 roms a long time ago but haven't used it since. At least not for roms and themes goes anyways. I still use it to flash Nandroids and such. It's still a great app, and I'm not nocking it. I just think that booting into recovery is more reliable.
If that doesn't work for you then start checking the forums for a fix. Or maybe start your own thread asking people for help. I'm not sure how to fix the problem myself cuz I've never come across it on my phones. I am sure that it isn't the theme that is causing the problem though. If you ever get it figured out then please stop back by here and let us know how you fixed it.