I have OL2003 prof installed on Windows XP prof. Email messages in my Inbox from a certain date and back, cannot be deleted. Only the ones in my Inbox, other items and whole folders can be deleted fine. When I delele a message from the Inbox the following pops up: "The messaging interface has returned an unknown error. It the problem persists, restart Outlook." When I try to move the message to the deleted item box, I get "Can't move item." When I do SHIFT + delete to pass by the deleted items folder, I get the same "unknown error" message. My pst file was big, so I deleted lots of items and folders and it's now 118 MB. I ran inbox repair tool and after a few times (!) there was nothing to repair. I checked for Office updates and installed the latest service pack and security update. I searched the net but can't find a solution for this exact problem. Is it something to do with Unicode maybe? What can I do? Thanks in advance!

I was having the same issue until I figured out what might be causing this. There was a corrupt email or old folder in my deleted items folder. I emptied the deleted items folder and was able to delete and move emails around as needed. Hope this works for you.