XPCOM - One machine only

Hi all, I have Firefox Portable version 53.0.2 on my external harddrive which I use every working day. I have to switch between two computers each day. The odd thing is that one of my computers has just started giving me the 'Cannot read XPCOM' error. This machine has opened Firefox Portable everyday before without fail, and the update was a while ago. As far as I can see there is nothing different on my machine that would have stopped it from loading Firefox.

If I install a new copy of Portable Firefox on that machine I get an access error code (something like 0xc0000022). If I take my drive to my other computer and start up Portable Firefox then all is fine.

Does anyone know what could be causing this please, and how to fix it? It seems to be something on that particular machine as I tried a friends usb drive with Firefox on it and that wouldn't start either.