Report net -- Using Paramerters in the group filter condition

[sunnyshore]

Hi,

i have created a report in the report studio, using the Tabular Sql.and i'm trying to add some filters for the reoprts by using the group filter option.. and i'm trying to user the parameters in the filter condition ..so that while the report is running it would prompt for the filter values..
for ex: [Product_category] = ?Product Category? -- in the expression editor it's validation successfully!!!!!

but when i'm running the report its giving the following error!!!
Experssion Parsing error.
[Product_category] is not defined...

but when i use th same above filter condition with some constant value ,without the parameter its running fine..

Can someone please advice me!!!


ur help is greatly appreciated...
Thanks
Sam