My two cents for SQL Reporting Services

Working with SRS200 this few weeks, some of the trouble wasted me few hours to solve it.
So share some of the issues you might be looking for it.
Index was outside the bounds of the array









This error pop when I hit view report after I had changed the fields included in report. Click refresh button in preview mode remove the error.
It is cause by the report cahce previous columns in preview mode.
The report parameter is read-only and cannot be modified.
The Report parameter is set to read only, for SRS2005, this can be happen when you checked the Internal checkbox in report parameter screen
How to use RowNumber in grouping matrix table
put this expression in the row grouping 1st column.
=RunningValue(Fields!NAME_S.Value,CountDistinct,Nothing)