You have specified a type variable DataRow[]called drProcess, but have not yet created an array of DataRows into which you want to place any values. Instead, you tried to tell the compiler that the string you are retrieving is actually a DataRow, but it is not.
, DataRows, DataRow . , , , . , objds.Tables[0].Rows DataRows. , .
, , var processes = new List<string>(), process.Add(objds.Tables[0].Rows[i]["ProcessName"].ToString()).
, .