Unreadable Message Glitch

[AkumaTsuki]

I recieved a new PM the other day howver when I went to read this new message I just recieve this "This message has been removed by its author before it was delivered." I am unable to delete or do anything with the message so every time I log in or change screens I get the message about having an unread PM.
It's a little annoying so is there anything that can be done about it?

 

[Trygon]

Click the box next to the PM. Scroll down to the bottom, click the dropdown box, and select 'Delete marked'.