Request for help regarding ClusterSupport

I am new to Jakarta Slide. I've just installed the Slide 2.1 Tomcat 5.0.28 
bundle onto two PCs (Windows XP, and Debian). I followed the wiki entry to 
set up clustering by modifying the Domain.xml on both PCs only:
http://wiki.apache.org/jakarta-slide/ClusterSupport

Both stores started and were accessible via a browser. However, no 
replication activity was seen.

The logs on both PC display "INFO: Poll for subscriber: 5,6,7,8" together 
with the
"WARNING:Login Exception Authenticating username null" 
"javax.security.auth.login.loginException: No user name Entered"

Could anyone give me a hint what I have done wrong or missed.

Thanks and Regards

Alex