Rdlc report field value fetch in c#

Hi,

 

i have a numeric field in rdlc report ,when i drag it into rdlc report,it automatic includes

sum(field.Gst,value,"DS_Invoice")

 

but when i try to use this,since i don't need sum value so i have used this following.

 (field.Gst,value,"DS_Invoice")

 

 Here,it throws an error

 

 The Value expression for the text box ‘Textbox29’ refers to the field ‘GST_SLAB’. Report item expressions can only refer to fields within the current dataset scope or, if inside an aggregate, the specified dataset scope

 

please help me ,how i will resolve this error.

 

Even i have used it in different way.

 (field.Gst,value)

 

it throws the same error