I have been having this problem with a Macbook Pro late 2006 and a Macbook Pro early 2011.
Macbook Pro refuses to mount an specific external hard drive or USB stick, after being able to do so with no problem before, and usually after the operating system disconnects it suddenly.
That particular external hard drive or USB stick is perfectly good since it works OK under linux.
MBP would mount the drive month later when tried again.
It have happen with two external Western Digital Hardrives (myPassport) as well as with a Kingston USB stick.
Disk Utility sees the drive but cannot mount it because it's "incompatible".
Many people seem to be having this problem and no solution has been found.
I cannot format the disk because that's where my backups are.
Again: a Linux box uses the drive with no problem. I don't have another mac at hand to try.
Now I'm going to buy another external hard drive from Amazon.
Which brand and model should I buy in order not ti have this problem again?