Upgrade issue from 1.5.5.1 to 2.1.0.1

My attempt to upgrade the opencart v1.5.5.1 site http://shop.yourownscrap.dk has failed, and I may be facing several different issues, question is how to proceed and what to do first?

The site is operated using PHP version 5.5. The Hosting center has recently deprecated an earlier version, versions 5.6 and 7.0 are also available, but I cannot log on the admin site with version 5.6, and the shop stops working entirely, if I switch to PHP version 7.0

If I switch on indication of PHP errors, I get this at the top of the page, when accessing the shop:
Deprecated: mysql_connect(): The mysql extension is deprecated and will be removed in the future: use mysqli or PDO instead in /customers/d/f/6/yourownscrap.dk/httpd.www/shop/system/database/mysql.php on line 6

I’ve been having long responsetimes for a while, and since mid December I’ve seen this in the error log with increasing frequency:

PHP Warning: session_start(): Cannot send session cache limiter - headers already sent (output started at /customers/d/f/6/yourownscrap.dk/httpd.www/shop/system/database/mysql.php:6) in /customers/d/f/6/yourownscrap.dk/httpd.www/shop/system/library/session.php on line 11

Recently the shop stopped responding – it turned out the maximum number of connections was exceeded. I’ve blocked one of the most aggressive robots from hitting on the site, it seems to have helped for now.

To try to fix the issues at hand, I decided to try and upgrade to the most recent version of opencart and downloaded 2.1.0.1.

Backup of the site and Upload of the upgrade patch went well, the install script was completed with success, but afterwards when accessing the admin page I get this:

Notice: Use of undefined constant DIR_MODIFICATION - assumed 'DIR_MODIFICATION' in /customers/d/f/6/yourownscrap.dk/httpd.www/shop/system/startup.php on line 72Notice: Use of undefined constant DIR_MODIFICATION - assumed 'DIR_MODIFICATION' in /customers/d/f/6/yourownscrap.dk/httpd.www/shop/system/startup.php on line 76…
Cannot send session cookie - headers already sent by (output started at customers/d/f/6/yourownscrap.dk/httpd.www/shop/admin/index.php:80) in /customers/d/f/6/yourownscrap.dk/httpd.www/shop/system/library/session.php on line 21
Warning: session_start(): Cannot send session cache limiter - headers already sent (output started at /customers/d/f/6/yourownscrap.dk/httpd.www/shop/admin/index.php:80) in /customers/d/f/6/yourownscrap.dk/httpd.www/shop/system/library/session.php on line 21
Notice: Error: Table 'yourownscrap_dk.oc_event' doesn't exist
Error No: 1146
Error in: /customers/d/f/6/yourownscrap.dk/httpd.www/shop/admin/index.php line 148
SELECT * FROM oc_event in /customers/d/f/6/yourownscrap.dk/httpd.www/shop/system/library/db/mysql.php on line 55Notice: Trying to get property of non-object in/customers/d/f/6/yourownscrap.dk/httpd.www/shop/admin/index.php on line 150Warning: Invalid argument supplied for foreach() in /customers/d/f/6/yourownscrap.dk/httpd.www/shop/admin/index.php on line 150

After login to the admin page I get a long list of similar error messages and cannot proceed.

Have restored the original version 1.5.5.1 version and the old database, and shop is up again.

Any suggestions on how to proceed?

How to proceed.....

Don't upgrade on a live site.

Next.... Look in the forum about upgrading. You will see your two issues and In LOTS of topics.

You will have a lot of things to contend with when you try to upgrade...
1) Not a complete upgrade script
2) Template compatibility
3) VQMod / OCMod compatibility
etc. etc. etc.

So I would suggest you read the forum about issues upgrading and see if you can do it yourself or need to hire someone.

Mike