Okay, so I'm installing/upgrading my installation of mIRC to 7.34 from 7.32, and now it's popping up a box asking for a password.
I've looked through the .ini files to figure out why. All of the other installs don't ask for passwords, only 7.34.
I will leave my original post in case someone else has the same problem, and search terms match...
I looked in the options of 7.32, and discovered a checkmark in "Other > Lock > Ask for password / On Startup"
I cleared the check and now 7.34 works fine.