can't enable View pages as tabs in cognos 10.2.2

[Pippa]

I am new in cognos and faced 2 issues below  :(

1. I have 3 pages in cognos report studio 10.2.2, now i want to view in 3 tabs instead of.
Then i click file > report properties. And i can't click on "View pages as tabs" (it's invisible)
So, can you help me ?

2. If I don't use option "View pages as tabs" , I use "Tab control" in Active Report, i can create tab.
So how difference ?

Thanks very much.

[BigChris]

Have you got a page set in your report?

https://www.ibm.com/support/knowledgecenter/SSEP7J_11.1.0/com.ibm.swg.ba.cognos.ug_cr_rptstd.doc/t_rptng_view_pges_tabs.html