I go back and forth between a mac and pc with no issues. Instead of trouble shooting this, I'd recommend reformatting the pilot (and sd card if you have one installed) on your pc in FAT32. If this doesn't fix it and your mac trouble shooting skills are limited, download and run a program called MainMenu (swee link below). It's a free and automated maintenance program for the mac. It may or may not help but it's worth a try. I suspect this has something to do with the permissions you have set for your mac so if the two options above don't work, I'd head to one of the mac forums for help. One other thing: for some reason, the pilot is far more suseptible to file corruption when disconnecting from my mac without ejecting first. You should never disconnect without ejecting from a mac or pc anyway.