[imp] problem sending mail

[Ole]

Redhat 7.3
Horde 2.0
Imp 3.2
Exim-3.36-2
Using imap

I can send/recive mail with outlook express in one of the windows computers
in the network. But with Imp i can only recive, and when i try to send i get
the error msg:

Fatal error: Call to a member function on a non-object in
/usr/share/pear/Mail.php on line 52


from file /usr/share/pear/Mail.php on line 52:

    return $this->raiseError('Unable to find class for driver ' , $driver);

---------------
maillog:

Mar 20 16:16:38 jonas imapd[30575]: Authenticated user=sivly
host=localhost.localdomain [127.0.0.1]
Mar 20 16:16:38 jonas imapd[30575]: Logout user=sivly
host=localhost.localdomain [127.0.0.1]

127.0.0.1 is the localhost and the server is running on this.

---------------
In the file /var/www/html/mail/horde/imp/config/servers.php

I have this:

$servers['imap'] = array(
    'name' => 'IMAP Server',
    'server' => 'localhost',  <-- it is this computer the server is running
    'protocol' => 'imap/notls',
    'port' => 143, <-- yes this is open
    'folders' => 'mail/',
    'namespace' => '',
    'maildomain' => 'gurustation.hiof.no', <- this is right
    'smtphost' => 'mail.gurustation.hiof.no', <- this is right
    'realm' => '',
    'preferred' => 'true'
);

+ some more stuff..

is there something more ?

-Ole