[imp] IMAP login fails

[Jaz]

I can't login to IMP.

I had a running system on Apache 1.3.9 and PHP 4.3, but decided to 
upgrade to Apache2 and PHP5.  After the upgrade I couldn't login to IMP.

Despite the imp test succeeding (successfully logs in and shows my inbox 
count, etc), and I can login to Horde fine, imp login fails and the 
following appears in horde's and my IMAP server's log:

HORDE.log:
Aug 01 15:27:58 HORDE [error] [imp] FAILED LOGIN 192.168.1.101 to 
127.0.0.1:143[imap/notls] as jaz [on line 237 of 
"D:\HTSERV\HTDOCS\horde\imp\lib\Auth\imp.php"]
Aug 01 15:28:11 HORDE [error] [imp] FAILED LOGIN 192.168.1.101 to 
127.0.0.1:143[imap/notls] as jaz at blah.homeip.net [on line 237 of 
"D:\HTSERV\HTDOCS\horde\imp\lib\Auth\imp.php"]
(nor does it work with "notls" omitted)

I also can't login to my remote POP3 server either:
Aug 01 15:28:43 HORDE [error] [imp] FAILED LOGIN 192.168.1.101 to 
mail.blah.net:110[pop3] as jaz [on line 237 of 
"D:\HTSERV\HTDOCS\horde\imp\lib\Auth\imp.php"]

IMAP.log:
Connection from 127.0.0.1, Mon Aug 01 15:23:45 2005
Password failure, user 'jaz', from 127.0.0.1
Password failure, user 'jaz', from 127.0.0.1
Password failure, user 'jaz', from 127.0.0.1
jaz at 127.0.0.1: 0 sec. elapsed, connection closed Mon Aug 01 15:23:45 2005

This happens with both my older install (some months) and with the 
latest horde HEAD.

Does this sound like a PHP or PEAR problem? Apache2?
A bad session path?
Any other ideas?
TIA --Jaz