This seems to have happened after the machine updated to Win 11. The machine has previously been working fine for several years.
The update to Win 11 may be a red herring. The external IT support may have change something else.
The rights to C:ProgramDataPegasusOFM are not set to Everyone full access, but I can create and edit files in Notepad.
Does any have any pointers please?

Thanks
Colin