I think it's a bug in CS. I have it setup so that registered
members can edit and delete their own posts. There is no time
limit for editing or deleting. I've encountered the same thing on
the actual CS site too.
I went ahead and set a time limit of 4 weeks. Perhaps with a time
limit set, it will let you delete it. Can you try it now and let
me know if that worked? If that fixes it, I'll have to increase
it to accomodate group builds.
I think if someone has replied directly to your post, then you may not
be able to delete your post. I know that was an open issue with
CS and I know they checked in a fix that takes care of replies in the
next version.