So I finally took the plunge on my fashion week server and updated from 1.4.0.1 to the latest version. All seemed to go well, but I logged out of the admin section after doing a few depreciated fixes to make my old theme work, but guess what? I now cannot log back in.

I have tried ALL the fixes listed in the various parts and am not sure. I'm on Dreamhost and I get a memory error when I try debugging or logging it as per your suggestion. So am not too sure?

I can access my database via the control panel, but even deleting the full table within the DB does nothing.

It's a live site, so a little worried. Any suggestions would be appreciated. When I try logging in, I simply get:
There was an error logging in.

Check your username and password and try again.

When I click on the "I forgot my user / password" the Submit button doesn't appear to do anything.

I tried changing the password in the DB too, but that's also not working, so I put it back to a long string of random letters it was.

Any help greatly appreciated, will donate like a philanthropist for working solutions. LOL

ALL SOLVED!

How I did it. I found a "reset password by email" underneath the unworking option.

Entered username and captcha and voila, a link in my inbox and reset and I'm now in the backend working like always.

Thanks. I'll still donate. ZP is awesome.

Glad you solved it. The only other way would have been this otherwise:
http://www.zenphoto.org/news/login-and-password-problems/#forgotten-admin-password

Thank you again.

I'm no programmer, but next mission from this upgrade is to build a custom theme.