Interesting - just this week, this happened to me!
I have my own name setup in SEPM as an administrator. I use my normal network/windows/ad password.
Life was good - I've been logging into the console as me, using my regular password, and now this week, it won't let me in AT ALL!
Authentication failed.
So, I have to login as the default "admin" name of "admin" and the password I assigned when I first installed.
I access the console from my own computers.
I normally use the JAVA console since the web console is so painfully slow and has a bunch of holes and issues it's pretty much unusable (constantly crashing back to a tab's home page, etc.)
Anyway, I've been logging in as myself for weeks, now this week, I can't.
I've added a second domain controller, reset passwords, all sorts of things, it simply won't let me in as me, but will as "admin".
I've done nothing this week that I've not done before other than I deleted a W2003 server that used to be a SEPM server because I've built 2 new servers and they have been up for over a month now.
So for over a month, we had 1 old 2003, and 2 new 2008 servers. This week I decided to go into SEPM, remove the server from the list, delete it in the admin area, then uninstalled SEPM from the server.
That's the only change.
I've been loggin in through the NEW servers for weeks anyway, I specifty the name of the new servers in the console when I log in, so it's not like I was even using the old server, and it was shown as a priority 2 server, no clients on it either.