OK, I think I have a rough explanation for the problem: the Argyll utilities have a single work thread, so the window message loop is serviced only when a test window color changes. This isn't a problem in itself, since the test window is not meant to be movable or changeable, and it's only activity is drawing a new color. The problem comes with Win7 (and probably Vista) Task Manager, which above and beyond monitoring applications to see if they are responding to messages in their message queue (by periodically posting a "get icon" message to see how long it takes to get a response), they also shut down any applications that it thinks aren't responding, by preventing WM_PAINT messages! For some reason KatMouse exacerbates this by vastly reducing the time threshold at which Task Manager regards an application as not responding. I have a proposed solution compiled into these versions (by using a thread to service the window messages): <http://www.argyllcms.com/ccmxmake.zip> 2131771 bytes See if they behave any better. Graeme Gill.