How to remove accounting files in the Windows port of FreeRadius?

Hi all, I've gotten FreeRadius on Windows (via the FreeRadius.net distro) up and running fine (thanks to all who helped with the setup details). Now I'm trying to purge old accounting records off the directory. Then I realise the files just cannot be deleted... Does anyone have this problem? I suspect it's to do with the 0666 permissions, which I have reset everything to 0777. But that does not seem to make any difference. Please help...thanks.