Here NetWtGreaterThan0 is a boolean report parameter. If value of NetWtGreaterThan0 is true than i want to show rows with Net Wt. Difference>0.000. Here Net Wt. Difference is calculated column.
Give this a try.
In the Row Visibility, Show / Hide based on expression.
=IIF(Parameters!NetWtGreaterThan0.Value = False, False, IIF(Net Wt. Difference>0.000, False, True))