On a regular basis, If I am using the back arrow key to move the cursor backwards in a scan, I can go a ways and then the cursor stops and a Windows error box pops up.

Unhanded exception has occurred in your application. If you click Continue, the application will ignore this error and attempt to continue. If you click Quit the application will close immediately.

Index was out of range. Must be non-negative and less than the size of the collection.
Paramater name: index.
If I click continue, then continue to hold the arrow key sometimes I can keep moving the cursor. Other times the same box comes up again.

What does this mean?