Upgrading 1.3.9 -> 1.5 + remove maintenance mode manually

Hello,

I have 2 problems:
-After upgrading to 1.5 version I can't access to the admin panel, it gives me this error "ERROR_SECURITY_ERROR" I tried to follow this thread but I don't really understand what should be added or modified.
-My web site is still in maintenance mode and I have a message in the front end that I would like to get rid of. Can I remove this maintenance mode message even if I can't access to he admin panel ?

Thanks a lot !!

Search for ERROR_SECURITY_ERROR here in the forums and you'll see several threads with possible fixes.

I can think of ways to remove the maintenance message and get your site out of maintenance mode, but the best way would be to get your admin working.

First, if "ERROR_SECURITY_ERROR" is displayed, then you're missing the updates to the language files, since your language files are missing the definitions added in the newer version.
That's the first place to start ... and while you're at it, re-check ALL your files and finish upgrading everything that was missed the first time around.