[imp] IMP Login Failures after PHP recompile

[p.g.]

Hello all, I'm hoping someone here can help with my problem.

Here's what I did:
1. I have a Plesk/Redhat linux server which came pre-configured with working
horde, php, apache, etc.

2. For various reasons, I needed to upgrade PHP to 4.3.2.

3. Based on advice I got in the plesk forum, I also grabbed the latest
courier imap, compiled it with no SSL.

4. I compiled PHP with imap.

5. After completing, everything else worked, but when I went to try and
login, it failed, and this turned up in the horde.log:
------------------------------------------
 "FAILED LOGIN xx.xx.xx.xx to localhost:143[imap] as peter [on line 270 of
"/usr/local/psa/home/vhosts/webmail/horde/imp/lib/IMP.php"
------------------------------------------

What I've done so far to try to fix:
1. I did a little reading, and found a recommendation to edit servers.php to
use imap/notls instead of imap. Ended up with the same exact error, except
with imap/notls instead of imap. No luck.

2. I ran the test.php script, which reports everything is okay with PHP. I
then ran the IMAP test and it fails " Couldn't open stream ".

3. I tried telnetting into my server:
-------------
#>telnet servername.com 143
#>1 login peter XXXXX
* PREAUTH [CAPABILITY IMAP4REV1 IDLE NAMESPACE MAILBOX-REFERRALS BINARY
UNSELECT SCAN SORT THREAD=REFERENCES THREAD=ORDEREDSUBJECT MULTIAPPEND]
Pre-authenticated user popuser servername.com IMAP4rev1 2003.338 at
------------
As I understand it, the response I was supposed to get is "Login OK" -- I'm
totally lost with that "preauth" stuff.

...

So, long story over -- anyone have any idea what I did wrong?  I've been
reading posts for hours and I don't even know where to look for errors.

Thanks for any help/advice.