I am trying to upgrade Moodle 2.7 to 3.1.But for some reason I can't. This is the error:
Coding error detected, it must be fixed by a programmer: The data source class does not exist.
Debug info:
Error code: codingerror
Stack trace:
line 498 of /cache/classes/definition.php: coding_exception thrown
line 515 of /cache/classes/helper.php: call to cache_definition::load()
line 480 of /cache/classes/helper.php: call to cache_helper::purge_store()
line 323 of /admin/index.php: call to cache_helper::purge_all()
What could be the problem of this?