Hello Pete
I tried your suggestion
"You might get away with simply installing FSX SP1, testing FSX, then re-boot, install SP2 and re-boot. Then try installing FSUIPC again. If that doesn't work then I've no easy fix. If you can roll back to a Windows restore point when it all worked, that might be a solution. Otherwise it may need a complete Windows re-installation."
No joy with this.
Next I tried downloading FSUIPC 4.624 and substituting the .dll file, again no joy.
Now I am going to bite the bullet and do a reinstall of XP.
I have a second computer (slow one) which has all my backed up files so I can use this for everyday activities, internet etc.
Pete I wonder if I may presume on your help with a bit of advice:
I can do the XP reinstall OK but after my experience with Simconnect I desperately want to avoid a repetition of my messing it up previously. Your advice on the order in which I should install the fsx installation and SP1 and SP2 would be helpful, eg. I think (as you suggested) I would install FSX then reboot then install SP1 reboot then finally SP2 and reboot then install FSUIPC, any other tips from yourself appreciated.
I am reasonably computer savvy but my age (83) has slowed me down somewhat but I have no qualms about the task so long as I can get the problem sorted.
Thanks Pete