Error message when posting

More than once when attempting to post I get the message -

"In order to try to prevent spammers, we do not allow our users to post URLs in any form until they have posted at least 5 legitimate posts and have been with us for more than 3 days. We appreciate your understanding in this matter in order to help us eliminate spam from this forum. If you have somehow gotten this message even though you meet both of the criteria, please let us know ASAP.

Thanks! "

Highly understandable -- except that when I get the error message there are *no* URLs in my post... besides that, I have been a member longer than 3 days and I think I've made more than 5 legitimate posts (or at least I considered them legitimate).

Any ideas?