Are you able to use a Command Prompt window to go to the directory and
manually rename the file:
erase domain.xml.bak
rename domain.xml domain.xml.bak
Is there any sort of special file management software on the system? It
sounds
like you have already eliminated the anti-virus software as a possibility.
I've seen Windows system get into a state where a particular file cannot
be deleted even though no process is accessing it. Rebooting windows
typically clears this. But it is strange that you are seeing this on two
systems.
Tom