Report item expressions can only refer to other report items within the same grouping scope or a containing grouping scope. Letters in the names of report items.

I had this question after viewing Displaying group data from a table in a textbox outside the table in SSRS 2008.

I followed the steps, and I'm at the point where I have a text box named Textbox52 in the header and it has the value I want, but when when I try to use Textbox52 to display the Value using the expression ReportItems!Textbox52.value  somewhere else in the report (I have several rectangles in the report), I get the error "Report item expressions can only refer to other report items within the same grouping scope or a containing grouping scope. Letters in the names of report items.