All, P210N driver but wanted to pass along as I too had this issue and my searching led me here.
I trashed two Terrain cards trying to do the latest update and after reading a variety of forums I called Garmin and did my time on hold. What was different for me was I tried to do a bulk update (selected both the 530 and 430 from the main screen and selected the Obstacle database for both). The first card appeared to update correctly but the second failed immediately after hitting go. I then went back and tried to update either again (doing the one card at a time) and both cards were now corrupt.
I was hoping to get them to send me new cards (as this is clearly a software issue) but they instead pointed me at a new utility they have that allows you to reset the card. Only downside is you have to dig up a Windows box if you're a Mac user as it only runs on Windows.
That said, it recovered both of my cards and I just downloaded new Terrain and Obstacle DB's to both cards (the utility wipes the card to recover it so you have to reload).
Hope it helps someone who reads this...
