Outlook Invitation Issue

Dears,

I am facing an issue in the outlook invitations.

the users cannot see the invitation in the calendar unless they accept it, if they did not accept the invitation, it will give them "invitation cannot be found" and when they accept it they can see it.

i am solving this issue by stopping one of the Hubcas servers (I have 4 hubcas servers working under network load balancer).

is there any way to solve this?

thanks

regards

Yousif