[imp] Installing Horde on Linux Server

[Star Trek Two]

Hello,
 
I'm trying to install Horde on a GoGrid Linux server.  The specific version of Linux
is Red hat Enterprise Linux Server Release 5.1, and I'm following the instructions
given at the following site:
 
http://www.horde.org/webmail/docs/?f=INSTALL.html
 
I've gotten to a point where I can go to the following URL:
 
http://<my-ip-address>:<my-port>/horde
 
and the Horde login page comes up.  I can then create an account here:
 
http://<my-ip-address>:<my-port>/horde/signup.php
 
and I can successfully log on to Horde using the account I've created.
However, to get into mail, Horde requires that I do a second login at a screen
entitled 'Welcome to Mail'.  Here is where I seem to be getting stuck.  When
I try to login I get the error message 'Login failed'.  
 
First off it isn't clear which login/password I should be using at this point.
The Horde login/password, a password on the Linux server, or...?  But
I've tried all possible combinations and permutations without success.  I've
also tried all four different IMAP servers listed on the Horde documentation
page as verified as working with Horde--again without success.
 
One challenge I have in troubleshooting this is I can't seem to find any logging
files--either for Horde or for any of the IMAP servers I've tried--and that
makes it difficult.  The message 'Login failed.' is not very descriptive of the
problem when that's the only thing I have to go on when troubleshooting.
 
Any ideas?
 
Thanks in advance!