@Emre: There has never been a key8s.dta in my GStudio7 folder.

OMG, I should have thought about posting the acklogs before. Then I would have noticed, that even if I set -diag in SED, the engine doesn't create an acklog, because it doesn't get the command line! Which means, it always tried to start like the Pro Edition would, which is of course unsupported by Com. If I use "Run" and start acknex.exe manually with "-sv -cl" or "-cl" it works!

Which means the acklogs are now irrelevant and the new bug I'm reporting is that SED doesn't pass the command line as set in preferences. Happens with A7.86.