Thanks to all who replied. I've just tried a new registry cleaner tuned up especially for Windows 7. The number of "errors" it came up with was amazing, well over 100, and it was a clean W7 install over the weekend.
Just in case anything was corrupted in this way, I have started 3.07 off and I'll see how long it lasts. I've never seen a disconnection like that on XP3. The cursor was free, the hardware telltale was green, and the little radar screen next to AirNav logo, top RHS, was still going around! Shutting it down seemed to leave it hanging, although it went off the screen! Attempts to shut the computer down reported ANRB still running. A "forced" shutdown didn't work. The only method left, the big switch, did work! The first 3 incidents I didn't actually see this morning, and the radar screen was empty with just a few entries left in the tables. The latest one I did see, and aircraft slowly went white and popped off the screen one by one. I had already disabled the "sleep" features and screen savers, so no problem caused by them. Other programmes have successfully run for over 12 hours, so something very odd.
Will revert back to a non beta version as soon as this one misbehaves to get a comparison for AirNav to work on.
thanks
Peter