Success at last. I was missing the VC2010 redistributables. In addition to that, a full reinstall was necessary. Now everything is working fine.
I did not have to switch tswriter.ax for mm1352000's version. Also there was no WinTV related service running, so I can confirm that it is safe to install "drivers only" from the current WinTV distribution.
Thanks everybody!
How did you update to miss this? The installer should have installed VC2010 redist.
Mark