Input sring was not in correct formate

Question

Hi i work in windows form application viusal studio 2008

I have windows form have two labeles label 33, label 34

label 33 represent quantity required

label 34 represent quantity shipped

if (Convert.ToInt32(label33.Text) == 0 && Convert.ToInt32(label34.Text) == 0)

{

Sales.SalesClass SalesClass3 = new Sales.SalesClass();

SalesClass3.DeleteProcessThird("Data Source=192.168.1.3;Initial Catalog=ALTAWI Group-Live;User ID=admin;Password=3210;Connection Lifetime=3;Max Pool Size=3;Connection Timeout=30");

}

problem when converting string to integer

it give me error excption

Input sring was not in correct formate

how to solve this problem