Why not to format your flash drive? Many important data is saving on this drive?
writes, your drive may be using different file system. So, you have to format it for changing the different file system.
So, in this situation, you are supposed to get back your important data on this drive with the help of a drive recovery freeware
and format this drive for using latter afterwards. Trust me! This freeware has ever recovered some inaccessible data of my cousin from a SanDisk hard drive completely. It can also works well on your flash drive for free. Warnings
: You should not save new file to rewrite your original data.
You should always back up your important data on a separate drive in the future.