It is a programme which tunes a radio receiver, so I wouldn't have known if the port was working with Putty.
The problem wasn't with the COM port but with the MSCOMM32.OCX file and other dependency DLLs.
As it happens, I found a more recent version of the programme and ran it. It failed as well, but I thought I'd give the old version one more
go before giving up, so I copied the .EXE for the old programme into the directory with the later install and it worked! The new install
somehow fixed the OCX.DLL problems.
Thanks to all who responded. SOLVED.
Cheemag