Weird Problems with WLBS on W2K3

Hello,

I have set up a NLB-Cluster with two nodes for the web application SQL
Reporting Services. The cluster is configured in Multicast. Each node has two
NICs configured. One for NLB, the other for the public network.
For some of our computers it is not possible to connect to the webserver. It
also not possible to make an telnet connection to port 80.
There is no firewall configured.
In the system events I get sometimes this warning:

Event Type: Warning
Event Source: WLBS
Event Category: None
Event ID: 18
Date: 16.06.2009
Time: 16:23:19
User: N/A
Computer: 2STORE-WEB1
Description:
NLB Cluster 10.5.150.142 : Duplicate cluster subnets detected. The network
may have been inadvertently partitioned.

For more information, see Help and Support Center at
http://go.microsoft.com/fwlink/events.asp.
Data:
0000: 00 00 0c 00 04 00 5a 00 ......Z.
0008: 00 00 00 00 12 00 07 80 .......€
0010: 00 00 00 00 00 00 00 00 ........
0018: 00 00 00 00 00 00 00 00 ........
0020: 00 00 00 00 00 00 00 00 ........
0028: 5c 05 06 00 01 00 00 00 \.......
0030: 00 00 00 00 ....


Any Ideas?

Thanks in advance.
Greets Matze