Hey there,
Yeah it needs you to know the previous password, thing is, i always knew it yet installation was blocking me from proceeding (in my case with Web Client for vSphere) as admin@SystemDomain, somehow using that precedure helped me reset it and the system was able to recognize it again.
We could say the SSO sometimes confuses its own password.
I hope it helps somebody later on that looks for a solution in a case like this.