Error Deleting Temp Files: Cannot Delete Folder

Hello respected members,
I am using Windows Vista ultimate.
The problem with me is that, whenever I try to delete temp files from my computer, I most of the time get error as below:

Error Deleting File or Folder
Cannot delete Folder: It is being used by another person or program
Close any programs that might be using the file and try again.
As these are temporary files, I don’t know which user or program is using them. I think that might be because of some virus. I am using Avira Personal Free edition of virus scan, and I did the scan for two times after updating the virus definitions, but no virus is detected inside my system.
I think that the system is compromised by the virus.
Please help me to get rid of it.
Thanks.
