The error would instantly reappear on OK or X! With no chance of running any thing else, effectively hanging the system.
Safe mode was little different.
A scan of various internet sites found that there has been numerous other instances of this error in the last weeks on similar OS.
As a consensus, Scanreg /restore from the dos prompt aided several posts, but not in my instance - past registry saves failed to load.
One post indicated that a file "Q1234..._DISK.dll" (where the numbers following the Q are random) were the cause. I located two instances of Q1790..~1.dll in C:\windows\, renamed them and the system is up and running OK.
AntiVirus scan did not detect this "infection".
Question from me is this a Virus, spyware or just malware?
I have no further knowledge on the infection other than is was around 5 July, site uncertain.