Unable to mount xxx Error msg

I created a Mint14 Boot USB stick to access the files on a non-booting desktop computer. The stick boots,but when I try to access the files, or any drive including the boot stick, I get the following message:

"Unable to mount 'xxxxx'

Adding read ACL for UID 999 to '/media/mint' failed: Operation not allowed."

This is my first attempt to use Linux for anything and I don't have a clue. This happens when booting my laptop with the stick.

Thanks for any help.

Gary