That error shouldn't affect PM's, it should be raised when a member tries to email another member. Do you know if its caused when you try to email a user from the profile page, topic page or send to a friend ?
It was one of a few measures introduced recently to prevent all the 419 advanced free fraud. Something similar will be introduced for private messages in the future. There may be a bug or two which will need to be addressed so any further info you have would be helpful in tracking it down.
It happens when I click on a members name and the little pop-up window appears on the left. So I guess it would be when it comes from their profile page. For the "Private Messages", everything is working fine. My forum moderator has the same trouble, and we are just trying to figure it out. Thanks!
Its actually working as it should. You should have received a test email from this board. I'll increase the character count to 300 and try to include a javascript style checker which decrements a visible number on that page so you know how many characters are left while you type.