The question of “setting message flags”

Increasingly, whenever I attempt to move a message from my Inbox to one of the folders I have set up to archive my mail, I receive a message stating, "Setting Message Flags".  It is a message that frustratingly lingers until the Windows Task Manager is finally used to stop it, at which point, Windows Live Mail shuts down altogether - leaving the message I wanted to move still in my Inbox when I subsequently reopen the program.  What is the reason for this message, and how I can prevent it from recurring?