our forum (version 1.9.4) suddenly started to give error messages when sending PM's. Only administrators are able to send PM's, but any other user gets an error message like this:
Your Private Message box is full. Maximum allowed is 2147483647. Please delete messages to free up space.
Number of allowed messages depends on user sending the PM, moderators have that amount and normal users have less. For example user who gets that error message does not have any PM's in his inbox. If I give that user administrative rights, he can send PM's succesfully.