Forticlient 6.0 will not install

I have a remote that who we cannot install forticlient 6.0 for. It detects an old installation and offers an option to Upgrade, if you follow the prompts it looks for an MSI which I have copied to the relevant location, but the install will not complete.

a colleague had setup an install via GPO for users in the office (on an IPWAN) and this laptop was probably in an office connected to that previously. I expect this has caused the issue - but there are no signs of Forticlient being previously installed on that machine.

Any suggestions appreciated.