have you done a signal-event post-upgrade and reboot? try repeating this upto 3 times - i've seen it reported in these forums that this can do the tricks for a number of errors.
if so then "report bugs and potential bugs in the bug tracker"!
i had no problems with any of the updates, if this knowledge helps.
in the meantime if you have done the post-upgrade and reboot
is the error on first entry to the page? or after trying to login?
after trying to login - different usernames?
just my 2c worth