I've found a couple of files where this happens as there is an illegal character in the filename that you are not stripping prior to trying to save the part
its a double !! character, stored in the nzb as –
I cannot even paste it here as the forum wont allow it, so I'm PM a download link for a nzb file to Quade
Im using 6.40 (2059) x64, Windows 7 x64