I'm not sure what value you are showing in the drpSchoolOffice.Text control but I am guessing you don't really want the droplist's text but you actually want the droplist's selected value. Try this...
int.TryParse(drpSchoolOffice.SelectedValue, out idS);
blUser.addUA2(idUser,idS,
txtLastName.Text.ToUpper(),
txtFirstName.Text.ToUpper(),
txtMiddleName.Text.ToUpper(),
drpUserType.Text,
txtUsername.Text.ToUpper());