I dislike CW (and yes, I've used it), but it's not a CW problem. It could be a ROM Manager flashing problem (it's legendary), and flashing SPRecovery fixes it so ROM Manager can push CW, but with FroYo came the RRS and a new bootloader and we have to turn the RRS off or we see this.
The way to tell is if you have NO recovery it's a flashing issue. If you see stock recovery it's RRS. No recovery is resolved fastest by flashing alternate recovery in RM. Stock recovery requires shutting the RRS down.