AddWithValue returns Null value

Hi,
cmd.Paramaters.AddWithValue retuns a null value.
from the below code when i get value from txtempid i can see the value but later when  i check the datase it returns no data.
Note: when i pass the value as   Select * from assignment where Client_ID=@empid retuns no value and where as when i pass the actual value at the place of @empid   eg. 'CL001' then returns value.  Select * from assignment where Client_ID='CL001'

GridView gv_Child = (GridView)e.Row.FindControl("gv_Child"); string txtempid = lblEmpID.Text; DataSet ds = new DataSet(); conn.Open(); string cmdstr = "Select * from assignment where Client_ID=@empid"; //string cmdstr = "Select * from assignment where Client_ID='CL001'"; MySqlCommand cmd = new MySqlCommand(cmdstr, con ...