I need to conditionally format the value of a text control on my main report based upon a value returned in my subreport.

On my main report I have a text box with the following in the Control Source property:
=IIf(Reports!r_Index_Info_Sub!txtTabCount>0,"Indexes","")

The control Reports!r_Index_Info_Sub!txtTabCount is returning a valid numeric value.

The control on my main report contains #Name?.

How can I properly reference the value in Reports!r_Index_Info_Sub!txtTabCount?