cannot add port rule to NLB

Hello,

I have set up two Exchange 2010 CAS + HUB in a NLB cluster. ( W2K8 R2)

I added some port rules: 25, 587, 995, 993 (All TCP traffic related to email, as you know).

The thing is that I want to add another port rule, and then I go to"Host Properties" \ "Port rules" , and there I see the ones I have created so far,  but the "add" button" is grey , not enabled.

I am logged in as the Domain administrator, and it was me who created the nlb cluster with the same user.

I am new to NLB, so I am probably missing something.

THANKS IN ADVANCE!

Luis Olías Técnico/Admon Sistemas . Sevilla (España - Spain)