Do you have an external SD card? The CWM installed through rom manager needs an external SD card to function. If you have a card and it is still fighting you, backing up, reformatting to FAT32, and restoring has been reported to fix it as well.
If you're using the spectrum exploit, make sure that you have matched the exploit to the stock ROM version you are using. There is one for gingerbread and one for ICS. It may take a few tries.
I haven't had time yet to get a source-built CM10 that boots, so I have a weird build environment based on a quattrimus spectrum ROM with the patches applied via script. After front cam gets fixed, the beta builds should hopefully come out of an actual CM source build.
I have a external sd card. I'll try the exploit for spectrum on ics. Thanks for the concern, will post results.