JavaMonitor doesn't communicate with instance

Hello,

My deployment configuration is:

XServe with MacOS X Server 10.2.8 and WO 5.1
WOAppA: one instance on port 2001
WOAppB: one instance on port 2002

WOAppA is ok. I can start and stop this instance via JavaMonitor and I 
see its statistics.

I can start the instance of WOAppB, but I can't stop it via 
JavaMonitor. Its transaction count and Active Session count on 
JavaMonitor did not change. The instance is running without any problem.

It seems that JavaMonitor unable to communicate with the instance of 
WOAppB.

What is the problem? Any ideas?

Thanks,
Karoly