I finally found a solution and could recover the access to all the folders in the USB Flash (And all their content). Downloaded a USB Virus protector and cleaned it. Since I downloaded the trial version, the program detected the problem in the USB and suggested to purchase the full version (US$25.95). Not much money, comparing withe the value of the information I though was lost.
Anyway, I appreciate the good intentions guys. I hope this information help many others later.
Thumbs up for this software! Free Download -USB Virus Scanner