what does this errro means

The Value expression for the text box ‘Textbox2’ refers to the report item .  Report item expressions in a Page Header or Footer can only refer to 
report items within the same ReportSection. Letters in the names of report items must use the correct case.	

what does this error means?Anybody knows

It means that you are either trying to retrieve a value from another section of your report from the header or footer; or you are mistyping the item that you are trying to use.

Please mark as answered to provide others assistance when they stumble upon similar problems.

Thanks.

i m trying to put thsi expression  in report header, what is the solution for this

Why don't you list the expression you are putting in the report header and tell us what the ReportItem value represents?