Hello @qbrd!
Yeah, Windows doesn’t handle MIDI ports well at all.
You can only open a MIDI port in one application at a time, so mainly that’s what’s going on (I have the same issues).
To use Kilowhat in Windows, you need to close every app using MIDI ports that might hold them open. I think ableton closes them so other apps can use them, but it seems it’s not working for you.
We added the “None” option to the MIDI ports list in Kilowhat, to close all the open ports, but there’s still something we haven’t yet figured out and it’s still not working properly.
The issue with the block 0 alert you got is something we detected and corrected, but still haven’t pushed the changes, but if you try again it should work.
Kilowhat is only supposed to list your Yaeltex controllers, not any other MIDI ports. For this, it sends a sort of “Hello” to all the MIDI ports and waits for a reply. Only Yaeltex controllers will reply correctly, and we’re supposed to close all the other MIDI ports, but like I said, the combination of Windows OS having this limitation for MIDI ports and this handshake process has its subtleties and we’re still sorting them out.
Also, sometimes, Kilowhat will freeze the browser, and like you said, removing USB will get it back up. Another bug we’re aware of and still investigating.
The safeguard message is a good idea, we’ll take that into account and see if there is a way to detect that the ports are open by other applications.
Thanks for reporting all this! Really helps us focus on what we need to work on 
And thanks for the patience!