[horde] ldap errors.

[Mauro]

I've configured horde to use ldap.
When I connect to imp for the first time I've these errors:

Notice: Undefined index: hordeprefs in /usr/share/horde2/lib/Prefs/ldap.php on 
line 372
 
 Warning: Invalid argument supplied for foreach() in 
/usr/share/horde2/lib/Prefs/ldap.php on line 378
 
 Warning: Cannot add header information - headers already sent by (output 
started at /usr/share/horde2/lib/Prefs/ldap.php:372) in 
/usr/share/horde2/imp/redirect.php on line 103

but if I reload the page it's all ok.
Then when I reconnect with the same user I have no errors.
In your opinion why I have errors when I connect for the first time?
Thank you.

Mauro