Error Message "Dynamic user groups can't be assigned to user" doesn't disappear after deleting contact

[four2six]

I edited a user and accidently assigned the user to a dynamic group (as the only group). The error message "Dynamic user groups can't be assigned to user" showed up, the user had no user groups assigned. i tried reassigning the "old" groups, but no luck, the error mesage remains. even after deleting the contact, it doesn't disappear. I cleared the browser cache, no change. I'm on the latest UAM. What causes this error? Can i manually fix it by deleting an entry in the databse? I can't give access to my site, so I'm looking for the reason behind that message. Generally it seems like a bug to me that I could accidentally assign a dynamic group to a user if it's not allowed.