Mal,

>My problem: The application runs fine at first. However, when I leave it running over night, the polling is no longer every second but every 3~4 seconds (despite it's timer interval at 1 second), the mouse works but the hour glass persists, and clicking on buttons takes a long time to register: about a minute.

Just a troubleshooting tip: try to eliminate anything that might interfere, such as a screen-saver. Be sure no other programs are also running on the same machine. Any scheduled activities, even automatic ones by the OS, like disk optimization, etc, that might kick in during the night? Automatic backups?