This is another entry for the "I hate computers" section. I had noticed that Fldigi for Windows did not appear to be remembering the "use software PTT" setting, so the first digimode transmission of a session always went no further than the sound card and I had to open the configuration settings and set it again. Thinking that this was probably a bug that had been fixed by now, I went to the Fldigi website and downloaded the latest version, which was 3.12.3 at the time or writing. After I installed it, the program froze on start up and never even appeared on-screen. I had to use Ctrl+Alt+Del to terminate it.
Some people probably think that because I can write programs this kind of thing is meat and drink to me. In fact I find it just as annoying and frustrating as anyone else. Although my experience means I have more ideas about what to try, I certainly don't immediately know the answer. And the onset of senility means that I often forget something obvious which means I waste a lot of time searching in the wrong place for the cause of the problem. I wish computers would "just work" like any other appliance!
So after half an hour that I would have preferred to have spent testing my loop antenna I eventually discovered that the problem was caused by the fact that I am using the Eterlogic Virtual Serial Port Emulator. If you have not come across it before, this is a bit of free software that allows more than one program to connect to one serial port at the same time. It has become an invaluable component of the computer side of my radio station as it allows my logging program, KComm, to be connected to my K3 at the same time as my remote tuning knob program, KTune, Fldigi or any other digital modes application.
VSPE is transparent to every application I have used it with so far. Even the Elecraft firmware update utility works through it, though obviously not at the same time as any other program. But something seems to have changed in Fldigi 3.12 so that it freezes when trying to access the virtual serial port, though it works perfectly when given direct access to the real one. Leigh, WA5ZNU has reported this to the developers so hopefully there will be a solution. Meanwhile I'm sticking with Fldigi version 3.11.