My personal message (PM) buffer is showing as being full; I had it reading as about 75% full this morning. I have deleted the whole second page of stored messages. It is still reading as full, so I can't receive or send anything.
Your previous account status allowed for a number of unlimited features. Now that you have a standard account, there are certain restrictions which one of them is Private Messages. You need to delete or clear all of your PM to free up space.