ok thank you all for your reply...
i followed the steps suggested by Tech and i still have the problem, i tried also to re-delete the repository subfolder (and reboot) and it didn't solve my issue... i cleaned my pc using CClean and atfcleaner and then i launched many anti-rootkits (blbeta, rootkitrevealer, combofix, gmer) and they founded nothing... i tried also to scan my pc using traditional anti-virus but AD aware SE, spybot and avast found my PC completely clean...
i dunno what to do now... do you still suggest me to open a post in "sysinternals"?
thanks again