I had the exact same problem. I couldn't for the life of me figure out how it happened. then I reread the requirements and noticed that zend.ze1_compatibility_mode had to be off. I ran phpinfo and saw that it was ON.
Once I modified the php.ini file, the problem was completely resolved.
So, if you're getting an error that contains
"Call to a member function xxxxxxx () on a non-object..."
You may wish to run phpinfo on your server and see if zend.ze1_compatibility_mode had to be off. If it's not, you have to change that.
It worked for me.