Another installation is in progress

Trying to install using the 18.00.18 version (posted 18 minutes ago :-)

I get the "Another installation is in progress. You must complete that installation before continuing this one". I terminated the install, restarted, get the same error.

There are no Take Command or TCC processes running (at least none that appear in Process Explorer, anyway). Win7, 64 bit.
None that I'm aware of. I was trying to upgrade from v13 to v18. I had a 18.00.16 build from the weekend. When that failed, I went to the forums, and saw that you had *just* posted a new 18.00.18, which I downloaded. I tried it, and got the error.

I was looking for TCC/Take Command processes, and there were none. What process names should I be looking for?