Page not accessible after login

Hi guys

Strange problem started without any changes made to the shop.

When ever someone logs in, they can not access my page at all - not https or http.

Admin is not affected.

Where do I even start to look for a solution?

ledstrips.no

1.5.6.4
Fortis

I have tried to run standard template
I have turned off most of the third party modules

[Edit]

Error log is full of theese:

2016-04-26 0:07:39 - PHP Notice: Undefined index: sort_order in /vqmod/vqcache/vq2-catalog_controller_common_header.php on line 258
2016-04-26 0:07:39 - PHP Notice: Undefined index: sort_order in /vqmod/vqcache/vq2-catalog_controller_common_header.php on line 258
2016-04-26 0:07:39 - PHP Notice: Undefined index: sort_order in /vqmod/vqcache/vq2-catalog_controller_common_header.php on line 258
2016-04-26 0:07:39 - PHP Notice: Undefined index: sort_order in /vqmod/vqcache/vq2-catalog_controller_common_header.php on line 261
2016-04-26 0:07:39 - PHP Notice: Undefined index: sort_order in /vqmod/vqcache/vq2-catalog_controller_common_header.php on line 258
2016-04-26 0:07:39 - PHP Notice: Undefined index: sort_order in /vqmod/vqcache/vq2-catalog_controller_common_header.php on line 258
2016-04-26 0:07:39 - PHP Notice: Undefined index: sort_order in /vqmod/vqcache/vq2-catalog_controller_common_header.php on line 258
2016-04-26 0:07:39 - PHP Notice: Undefined index: sort_order in /vqmod/vqcache/vq2-catalog_controller_common_header.php on line 258
2016-04-26 0:07:39 - PHP Notice: Undefined index: sort_order in /vqmod/vqcache/vq2-catalog_controller_common_header.php on line 258
2016-04-26 0:07:39 - PHP Notice: Undefined index: sort_order in /vqmod/vqcache/vq2-catalog_controller_common_header.php on line 258
2016-04-26 0:07:39 - PHP Notice: Undefined index: sort_order in /vqmod/vqcache/vq2-catalog_controller_common_header.php on line 258
2016-04-26 0:07:39 - PHP Notice: Undefined index: sort_order in /vqmod/vqcache/vq2-catalog_controller_common_header.php on line 261
2016-04-26 0:07:39 - PHP Notice: Undefined index: category_1_id in /vqmod/vqcache/vq2-catalog_view_theme_fortis_template_common_header.tpl on line 390

Kind regards
Kyrre

but this is NOT OC v.1.5.6.4, as you mentioned, it's some OC-2, you use...
Ernie

IP_CAM wrote:but this is NOT OC v.1.5.6.4, as you mentioned, it's some OC-2, you use...
Ernie

Yes, I'm sorry. I was desperate - I started to set up 2.2 - and it all wen to h*ll I got an error after successfully importing products and customers, and then >I installed an Analytics script - and the page was unavailable again...

I've been running the shop for three years almost with no errors... and then this...

there is an old saying, never change a winning horse...
or, never touch a running Engine... , in modern words!
Ernie

IP_CAM wrote:there is an old saying, never change a winning horse...
or, never touch a running Engine... , in modern words!
Ernie

I know - but the 1.5.6.4 stopped working all by it self

I am close to getting it running. Combined a backup of all files with a backup of the database. Soon there