Firstly, thank you so much for a great Open Source program. My knowledge of web development is very limited and I've really enjoyed using OpenCart.
The web site I'm having problems with is for my sister. http://www.bmore.net/index1.php. Please note it's index1.php because there is already an old site there (http://www.bmore.net) which will eventually be removed and replaced with the OpenCart site.
The problem that I'm having is changes can be made in the Admin panel fine. If I then switch tabs back to the main site and hit refresh to view the changes I've just made, then switch tabs back to the Admin panel, I'm logged out and have to log back in again!

As I said, I'm very new to PHP, but I think it might be something to do with upgrading. When I upgraded from 1.3.3 to 1.3.4 I followed the instructions but this is when the problem began.
I'm more than happy to totally delete everything and re-install from fresh which will work fine but all the time my sister has spent loading her products into OpenCart will be removed!
I have tried replacing all the files in the directory with those from the OpenCart download in case it's a coding glitch that I've caused (which it probably is), but even after doing this the problem's still there.
I've not really done any customisation to the template yet so as I mentioned, I'm more than happy to delete the current site and re-install then start to customise again, but I really want to avoid losing all the work that's been put in so far!
Has anyone come across this issue before? I'm fairly sure that it's not a coding glitch else it would have been fixed by replacing all the files in the directory with the originals?
If anyone's got any suggestions of what I could try I'd really appreciate it. Failing that, how could I copy what's in the current database and all the images etc, and re-import these into a clean install - because my concern is that it might be a database glitch - and if i export & import via phpMyAdmin it's simply going to reinstall the 'fault'.
Any help would be greatly appreciated! Many thanks.

Barney.