Thanks! Good to know. I've been using Kaspersky for years and it never occurred to me to check if I still needed it.
I de-installed Kaspersky and the MC29 install that wouldn't launch.
I tried reinstalling MC29, also using "run as administrator" but the result was the same.
Although I am the only user and admin in any case, I created an admin account with the command prompt, logged in with the admin account and tried again. The only difference was that at the end of the install routine, I got a message saying MC29 had installed successfully and the option to launch it. Unfortunately it still doesn't launch.
I also tried installing MC28. Same story: install completes and MC28 is in the start menu, but doesn't launch.
I tried again on the other machine too. No luck there either. I still get the same error message about JRTools.