Since switching from LV 4.0 on W95 to LV 5.1 on NT, some exe's (made with the Application Builder) make other programs crash much more often. The vi's that cause the crash typically hog the CPU. The NT Performance Monitor shows near 100% CPU usage for the task. It is MS Excel which crashes, particularly while running a dialog box and associated VBA code I have written. The problem seems to virtually disappear (no more Excel crashes) if some Wait (ms) vi's are inserted in the vi to reduce CPU load. I've read that thread switching can cause crashes, but shouldn't the OS free me from worying about this?