[imp] error after logging into imp

[mlist]

I implemented horde/imp on my webserver to acces my mailserver with imap- 
ssl. I can log into the imp webinterface, but after I`m logged in I get the 
following error stating:

A fatal error has occurred:

'' is not configured in the Horde Registry.

[line 753 of /var/www/htdocs/horde/lib/Registry.php]

Details have been logged for the administrator.


What does this error mean and most important what to do about it?

Thanx,
Tijss