upgrading malfunction in startup.php

got the Versie 1.5.2.1 (dutch)
and tried to upgrade 3.3.0.6
got a failure in \system\startup.php, which says:

Warning: Use of undefined constant DIR_MODIFICATION - assumed 'DIR_MODIFICATION' (this will throw an Error in a future version of PHP) in .../system/startup.php on line 51
Warning: Use of undefined constant DIR_MODIFICATION - assumed 'DIR_MODIFICATION' (this will throw an Error in a future version of PHP) in .../system/startup.php on line 59
and this 4 times

line 51: $file = DIR_MODIFICATION . 'admin/' . substr($filename, strlen(DIR_APPLICATION));
line 59: $file = DIR_MODIFICATION . 'system/' . substr($filename, strlen(DIR_SYSTEM));

got the upgrade reversed
don't know what to do next
who can help?
noticed that the warning not to update config.php was strange because there were no such files in the update, only config-dist.php files

You should use the search in this forum here, too many posts and answers about this.

The OC upgrade from 1.5.x to a 3.0.x release almost certainly will fail. You are better off doing a fresh install of the new OC 3.0.x, and then use the Export/Import tool to move your category and product data over to the new server, see our FAQ on how to do it.

Good idea to work with the import/export tool.
but....
I discovered that the problem (I think) lays mainly in the fact that the php version is old and when I get the newest version installed the opencart program jams.
And of course... the import/export tool needs the 7 version instead of 5.6
I cannot figure out why opencart 1.5 refuses php 7.
I get when updated a HTTP ERROR 500 or 502 Bad Gateway on all items

I do however have a backup called: backup.sql, but know if that does the trick as well

and I did do several search attempts ...

The old V3.22 of the Export/Import tool should work for PHP 5.x.

thank you, JNeuhof, thta's a good idea
but....
can only find this one with your description: opencart-1-5-1-to-1-5-6-x-export-import-multilingual-3-22.zip
and that's the newest one.
Can't find a place older versions either
Can you (someone) help?

So what's the problem? V3.22 for older PHP versions, V4.7 for newer PHP versions, simple as that. All available from the OpenCart marketplace download.

Thanks!
Installed everything including the access rights.
But sadly no import/export to be found in the admin view.
Is there an other way to open import/export?

You probably haven't followed the installation instructions, see our FAQ.

I painstakely followed all the instructions
found the System > Users > User Group for the 'tool/export_import twice
the file /admin/controller/tool/export_import.php is found but gives a 500 error
the fault was in line 2: class ControllerToolExportImport extends Controller {

My site is in dutch and I noticed that export_import.php was only in the english directory, but that did not help

This has nothing to do with the language as it falls back to english if no dutch language file.

Ask your webhost for the server's error log entries for your Internal Server 500 error which which will have more details.

mod_fcgid: stderr: PHP Fatal error: Class 'Controller' not found in /var/www/vhosts/erobird.nl/httpdocs/winkel/admin/controller/tool/export_import.php on line 2
an Apache error
this is what you mean?

This error message is not an issue with the Export/Import tool. Rather, your 1.5. is corrupted somewhere because the 'Controller' clearly exists as one of the OC core classes at system/engine/controller.php.