Just try doing "Disk Fragment" your Flash Drive. I believe it may work for you.
Follow the following steps after you connect your "Flash Drive" on reverse side of your CPU USB Port:
1.) Double Click on "My Computer" (or "Computer" in Windows Vista)
2.) Right Click on "Flash Drive", Click "Properties"
3.) In the Pop-up window "New volume Properties", go to "Tools" tab
4.) Under "Defragmentation" click "Defragment now"
Now it begins Disk Defragmenting. Wait for sometime. When operation completes, reboot your machine and try accessing your Flash drive.
Please get back the result at your convinient time.
Thank you :)