'Server Busy' Error Message

[Billtog]

I keep getting this message that says "This action cannot be completed because the other program is busy. Choose 'Switch To' to activate the busy program and correct the problem. There are three buttons, "Switch To," "Retry," and "Cancel" (which I am unable to click). I click "Retry" and the same message pops up over and over again. If I click "Switch To," the start menu is opened, but the message stays. The main problems here are that this message will appear when I'm doing nothing at all (I'll be watching a video or not even be in the room and this message will come up), and that it won't go away unless I restart my computer. I would just move it somewhere and ignore it for the time being, but every time I press any button the message relocates itself to the center of my screen. Is there anyone that can help me out (I'm running Windows XP)?