Thanks for the responses guys. Unfortunately, I downloaded it via the web app link (i.e. from the right place).

I now have ControlMac running okay on a laptop from work, but that will only be good for this weekend.

Does anyone know what Meridian calls its plist files? Sometimes, for this sort of problem, deleting the plist files (or any other prefs) does the trick.

Living room: 818v3, Audio Research D150, Maggie 1.6
A/V room: 861v8, DSP7200SE L/R/C, 4x DSP320 surrounds, ID41 + Roon, UHD722, Prime+PS