[LMB] AKICOT:L - Mac mail problem

[Jacki Knight]

I know there are people on this list who know a lot more about my Mac  
than I do, so:

I was tidying up my mailboxes last night and now it won't let me move  
anything into the LMB folder and the Rule no longer works.

I used to have a hierarchy of a List-Mail folder and sub-folders for  
each list I'm on but I've changed it to separate folders only and  
deleted a few old ones I wasn't using.

Any time I try to move a message from my inbox to the LMB folder it  
comes up with a message telling me:

The message “[LMB] Cybook tips was re: The worth of Ebook readers  
OT:” could not be moved to the mailbox “Jacki/LMB List — On My Mac”
or the likes.

I tried re-building the mailbox but the problem remains. It doesn't  
happen with any other folder that used to be a sub-folder, just this  
one. Does anyone have any suggestions?

Jacki - frustrated - and stumped