[imp] Errors trying to send from the compose window

[fnord]

I'm running Horde 3.1 and Horde-Imp 4.1, on Apache 2 and php 5.0.5.

Everything is working perfectly except sending emails. When I click on 
"Send Message" I get these errors:

-------------------------------------------------------------------

*Notice*: Undefined index: mailer in 
*/var/www/localhost/htdocs/horde/imp/lib/Compose.php* on line *87*

*Notice*: Undefined index: mailer in 
*/var/www/localhost/htdocs/horde/imp/lib/Compose.php* on line *88*

*Notice*: Undefined index: log in 
*/var/www/localhost/htdocs/horde/lib/Horde.php* on line *49*

Error  There was an error sending your message: Unable to find class for 
driver

-------------------------------------------------------------------

The lines in Compose.php are:

      $params = $conf['mailer']['params'];
      $driver = $conf['mailer']['type'];

I've doublechecked my PEAR installation, and I've got PEAR-Auth, 
PEAR-NET_Smtp, PEAR-Mail and PEAR-Mail_MIME installed.

Can anyone point me in a direction to fix this/ It's driving me mad.

I've checked my php.ini file and SafeMode is Off, and file_uploads is 
allowed.

I'm running out of things to look for....


Thanks,
fnord