Sure, did you do a full wipe before installing the ROM?
It's OK if you didn't, just power off the device. hold down the volume down button and power button at the same time until the bootloader loads, select 'bootloader' then after that loads, select 'recovery' - then in recovery select erase user data, then go to advanced and wipe dalvik, then go back and go to partitions menu and clear out sd-ext, data, system, cache (again for luck, why not), then go back one menu and install zip from sd card, you'll have to browse to the clockworkmod directory and dig deep to find the zip for CM6.1.1
Or-
If you created a backup (nandroid), you can just go to restore in the main recovery menu and restore from that and re do it all again in rom manager but make sure to check "wipe data" when prompted.