[imp] conf['prefs']['driver'] question

[ragnar]

Hello.

One problem. 

If I allow the conf['prefs']['driver'] = 'sql'; in horde/config/horde.php to 
be uncommented I cannot log in via imap. Regardless of the fact that the 
database is there, and the other database directives are uncommented. When I 
comment this directive I can log in alright and send/receive mail but with 
warnings: Undefined index: driver in... 

I've tried to comment out the database directives an put 'none', 'session' 
or '' instead of 'sql' but without success. Only if this directive is 
commented I can log in. 

Any hints on this one?
Regards,
Ragnar.