Hmmm, interesting.
The next thing to try would be to try updating MapSource and then trying a different CF card in the 2610 (I guess this might be faulty)
Download the latest version of MapSource from here:
Garmin: MapSource Updates & Downloads
Then in order to check that the problem is not being caused by the Compact Flash (CF) card, I would suggest that you could try another on that you know works in the 2610.
Have you got a camera or something which also uses CF cards?
Has the map transfer to the card ever worked for you ar has this problem only recently started?
David