Very Many Thanks - All Solved:-)
Deleting the said registry key cured the window problem: I now have console control of the BBS again:-) :-)
and the bpq32.dll runs fine with the latest version of BPQMAIL.
Heavens only knows what I did to cause the disappearing window problem in the first place! I can only think I must have accidentally clicked on something!
I have also stored a copy of bpq32.dll with my library of install files as well as on my backup USB pen.
Thank you again John for your very prompt reply and valuable tech support.
All the best.