Zen Cart Suddenly wonky after server upgrade to PHP 5

my Zen cart site has suddenly come up with this error and is preventing admin log in

Fatal error: Call to a member function Execute() on a non-object in /home/username/public_html/includes/functions/sessions.php on line 72

I am wondering if it has to do with a server upgraded to PHP 5.2.5?.
this zen cart version is Version 1.2.5

Does anyone got any ideas where I should start on trouble shooting this? Should I try an upgrade to fix it, or will it make it worse!

Thanks!
Cori

Yes this is the issue,
you really need to upgrade,

This should help give some SHORT TERM relief:
http://www.zen-cart.com/forum/showpost.php?p=287587&postcount=26

But, as Merlin said, you REALLY DO need to upgrade, as there are other incompatibilities addressed in the newer versions.

Be sure to follow the upgrade steps carefully. You'll have to redesign your template since you're moving from such an old version ...

I am a little nervous about upgrading to tell the truth, I have no idea which files where edited and there were alot, I am hoping for a semi easy fix. I did look at the instructions which also look like many, many hours of work....alot of that "merging, seperate install folders, new databases....wow...looks like it could be easier to create a whole new cart with an easy script?

If I upgrade am I looking a days and a bug night mare? Or will it go easy? Is there a different way, is there not just an "upgrade" script?

Thanks for your help!
Cori

If you followed the rules governing templates in the begining then upgrading wont be that hard, its just a matter or merging your add ons in,

however it might be easier to create a brand new install in a new folder
then after the site is installed upload a copy of your current database, and run the upgrade scripts,

then reskin the new cart,
once done move it into place.

and no there is no upgrade script

You would probably save a ton of time just starting with a fresh install and upgrading the DB only. That would certainly be the fastest way to have your store up and running again.