Upgrade from 2.0.1.1 to 2.3.0.2

Hi,
I have gone through the upgrade process 2.0.1.1 to 2.3.0.2 and got the upgrade successful message at the end of it.
Then cleared cookies in my browser
Then went to the admin page to login, what I found was that it wouldn't recognise my username/password, then remembered I had a another admin login combination (the first I ever set up) and these allowed me into admin.
I followed through the rest of the upgrade instructions and then logged out and tried to log back in, still only works my with original credentials.
I did try to set up a new additional admin user but the system didn't remember it after saving.
So persevered using the orginal credentials, next I set the shop to the default theme in settings and save but keep getting the message no theme assigned to this store in the browser.

So am now wondering if I took too big of step when upgrading, perhaps I should have gone from 2.0.1.1 to a slightly newer version before going to 2.3.0.2, I did search for a recommended upgrade path but didn't see one.

Fortunately this has all been done on a dev server and the live site is still good on 2.0.1.1

Any advice would be really appreciated
many thanks
Dave

Hi Surely somebody out there has done this before, I would really appreciate some clues please
Thanks
Dave

Hi Dave,
What instructions did you use for upgrading? I'm considering an upgrade from 2.0.1.1. to 2.3.x.x too. Or did you already manage to solve this problem?
Cheers!
Marc