Thanks, zok & SD69. I'll give that a try.

I took a closer look at the SD card and I think the entire thing is corrupted. I mounted it on another machine and ran SHA1SUM on all the files. When I ran the SHA1SUM again, I got a different checksum on a dozen or so files.

It looks like my SD card is corrupted, so I'll probably need a fresh copy of the maps, etc. after all.

Wish me luck - I'll be contacting tech support this week.

Thanks again for the pointers,
- Steve