Hello,
The only thing I can think off to cause this behavior is that the settings file is read-only and it contains an old password now. The scenario is like this:
a) you defined your forums and so on, put passwords.
b) at a later moment you activated UAC (or something happened, and the settings file is not writable anymore by the app to update password or other forum values)
c) you changed your admin password, but the app can't update the new settings
d) now you have to type it everytime.
Seems a bit strange but ... who knows ?
You have two options:
a) if what I said sounds like what would happen, then please restore rights (or run as administrator).
b) if not, maybe you can try to start it from a command prompt and see if there are exceptions when starting up. Maybe the settings file got corrupted somehow in time and password is not usable anymore.