Modify the Save_Position method to return a bool value: true for OK, false for "an error occured"
Then check in your code:
objt.Position_Number = TxtPositionNum.Text;
objt.Grade = Txtgrade.Text;
objt.StartDate = TxtStartDate.Text;
if (objt.Save_Position())
{
Business_Logic.Employee obje = new Business_Logic.Employee();
obje.Position_Number = TxtPositionNum.Text;
obje.Cell_Number = TxtCellNumber.Text;
obje.Email = TxtEmail.Text;
obje.Save_Employee();
}
Alternatively, throw an exception in your Save_Position method, and catch it in the code which calls your fragment. It can then report a problem to the user.