[TYPO3-english] error in DatabaseConnection.php

[Peder Høy Kristensen]

I set up a new site ver 6.1.1. Everything worked quite well. But suddenly something went wrong. The formular for Frontend End users is not any more visible in frontend, and in the backend I get the following error message, when I try to open Extension Manager:

Fatal error: Call to a member function query() on a non-object in .../typo3/sysext/core/Classes/Database/DatabaseConnection.php on line 981

What does this error message mean, and what can I do about it?

Venlig hilsen / Best Regards
Peder Høy Kristensen