Question Call to undefined method JController::getInstance() in \...\components\com_users\users..php

Hi it's me again.

Seems, that the only thing that does not work are the user actions: login, forgot passwort, forgot username, register. See attached picture

All the links point to i.e. .../component/users/?view=registration.
When I copy these links and paste them in the addressfield and delete the 's' in 'users', I get the right page for the related action shown.

Question: Is it possible to edit a/the file(s) which contain subject links to work around this problem?

The issues reported in this topic seem to mainly focus on the fact that some people had tried to migrate from J! 1.5 to J! 1.6 and the migration failed leaving the site(s) in a disorganised state. The cause of this problem may have been in the way that the J! 1.5 -> J! 1.6 migration was undertaken. Do we know how that migration attempt was performed? Did it, for example, involve jUpgrade and, if so, what version was used? Did someone, for example, try to install J! 1.6 on a J! 1.5 system using the Extension Manager? Do you know anything more?