I upgraded some files and started the application. I was able to logon on my normal forum user. But, after I updated the "theme" I was logged out.

If I go to "forgot password" it says that the user does not exist. I have my user still in the User database. I assume there is some problem with the forum looking at the wrong forum/host/board or something like that but I know too little of where to look and change.

Any ideas?

Did you update the theme name?

If so, maybe try manually updating your forum user name with the updated theme name?