remove pen drive virus

Sir

If i use "Flash Disinfector" to remove virus in "Pen Drive" it shows "W32.silyFDC" & "Trojan.Dropper" cleaned by deletion in Symantec AntiVirus.

please explain this and i need to remove virus in my "Pen Drive". I cannot open and format my "Pen Drive"

I attached the error message shown to me for ur view. pls. see the attachment.

thanks and regards
r. dillikumar