Thanks for the reply.
I ran the cleanup tool. The txt result log showed 'no malwarebyte software installed on this computer'
(I had previously uninstalled Malwarebytes using revo-uninstaller prior to trying a fresh install)
I then looked in ProgramData - there was a folder there for another software product but that was all, no Malwarebytes stuff. There are no Malwarebytes folders in 'Program Files'.
I tried d/loading the setup file again with the same resultant error message.
I am using a win XP 32 bit system. There was no option at the d/load to select 64 or 32 so I assume 'one size fits all'?