Fatal error on line 12

dear all,

I upgraded my opencart to 1.5.1.2 latest opencart now al went ok but not this appears on my website.

Fatal error: Call to a member function link() on a non-object in /home/pztag/public_html/shop/catalog/controller/error/not_found.php on line 12

What does this mean?

What version did you upgrade from ?

I upgrade from 1.4.9.5 to 1.4.9.6 ok website working

Then from 1.4.9.6 to 1.5.0 everything went well also said the installation was succesfull. Then I wanted to log into admin then the problem shown:

Error: Unknown column 'store_id' in 'where clause'
Error No: 1054
SELECT * FROM web_setting WHERE store_id = '0' OR store_id = '0' ORDER BY store_id ASC"

I looked if anyone same problem and there was. So I follow "viewtopic.php?f=2&t=36519" and did step by step what was was in the readme.

No this problem shown: Fatal error: Cannot access private property Document::$title in /home/pztag/public_html/shop/install/controller/header.php on line 4

If all was correct i wanted to install right away 1.5.1.2 but need to solve this first.

I was incorrect just now the error is:
Notice: Use of undefined constant HTTPS_SERVER - assumed 'HTTPS_SERVER' in /home/pztag/public_html/shop/index.php on line 63

Fatal error: Class 'Url' not found in /home/pztag/public_html/shop/index.php on line 67

my website is www.kart-mall.com/shop