One of the servers in array block people

I have two ISA 2004 Ent. Servers members of an array, NLB integrated.
Users complain that sporadically access to OWA fail.

After troubleshooting this, I see that every time the connection to OWA goes
thru "ISA-Server1", the attempt fails (denied by Enterprise Rules).

Question is this, if the two servers are members of the same array, aren't
they supposed to process same rules ? What to do to determine how the
ISA-Server1 is getting screwed up and not processing the rule accordingly ?


.