unable to cast object of type 'system.int32' to type 'system

Question

unable to cast object of type 'system.int32' to type 'system.string' 

 

I got the above error, when i tried  the below line

 

 

int nOut = datatable.Rows.IndexOf(datatable.AsEnumerable().Where(c => c.Field(4) == lblFirst.Value && c.Field(6) == "0").FirstOrDefault());