Time machine not recognizing backup partition

I have been using a LaCie 500 GB external drive to backup my MacBook Pro with time machine for over a year. When I got it I set up a separate 30 GB partition with MS-DOS (FAT 32) format to transfer files between computers with different operating systems. Suddenly my OS (OSX 10.6.8) doesn't recognize the backup partition, but still recognizes the other one. So now Time Machine can't do its backups. Any ideas?

It sounds like your LaCie drive is failing. Open Disk Utility and run verify and repair on the drive.

Weird. When I tried again after getting your reply the backup drive showed up and I was able to backup with no problem. However, I did run verify and repair afterwards and it found and fixed several errors, so thanks a lot for you your suggestion!