Is there a mac app that can recover a suddenly unreadable thumb drive? it was working fine when suddenly I plugged it into my pc, & a message showed me that I needed to format the drive. I then plugged it into my mac & the same thing happened, it wanted to format it, it was showing as a blank drive. It was a fairly full drive, not completely full. I found disk drill, & the free version is no good, it will only recover if I pay a hefty $89.00 dollars for an upgrade to the "pro" version. are there any other truly free or under $50.00 apps that will find & recover my files?