AX2012 SSRS Dynamics Header Title Based on Different Tablix

Hi,

I have a report with three tablixes in the report body, each populated from different data sets. Each tablix is separated by page break.

This report is quiet complicated so I have to use different data sets to separate the data.

In the report header, I want to change the title dynamically based on which tablix is currently populating the body. 

I tried using Globals!PageName but got "Globals!PageName is invalid. InvalidProperty" error when deploying my report.

Why is it I cannot use this Globals!PageName? Is it not supported in AX 2012 somehow?

Are there any alternative way(s) to achieve this?

Thank You.