Adminer problems

Hi - I installed Adminer to do a backup. I installed it, and selected the Moodle database. Then selected "dump", and received the following error:

"Error: Database connection failed. It is possible that the database is overloaded or otherwise not running properly. The site administrator should also check the database details have been correctly specified in config.php"

Now I can't log into Moodle - it's stuck on the error message screen. Any ideas?

I am running Moodle 2.4.1, php 5.3.10, Ubuntu 12.04, Apache 2.

Thanks for any suggestions.