Problem in passing parameters in crystal report

Dear Friends

I am using crystal report 8's control in vb6. My report is attached with stored procedure which have two date parameters, when i am passing parameter values it returns error "invalid parameter values".

Code:

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Crt.ParameterFields(0) = "@firstdate; = '" & Format(dtStart.Value, "yyyymmdd") & "'"
    Crt.ParameterFields(1) = "@lastdate; = '" & Format(dtEnd.Value, "yyyymmdd") & "'"
    Crt.Action = True

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any solution plz

Regargs