How to get the value of the answer that computed by calling Mathematica function from .NET program?

Question

Imports System
Imports Wolfram.NETLink

Public Class Form1
    Dim kernel1 As IKernelLink = MathLinkFactory.CreateKernelLink()

Public Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click

    kernel1.Evaluate("<< StringConvertTools.x")
    kernel1.Evaluate("<< BearingCapacityCalToolBox.x")
    kernel1.WaitAndDiscardAnswer()

    MsgBox("数据加载完成", MsgBoxStyle.OkOnly, "提示")

End Sub

Private Sub Button2_Click(sender As System.Object, e As System.EventArgs) Handles Button3.Click

    Dim flag,flag1 As Integer

    kernel1.Evaluate("1+2")
    kernel1.WaitForAnswer()
    flag1 = kernel1.GetInteger()

    kernel1.Evaluate("flag=1;While[Excel[""A""<>ToString[flag]]=!=Empty,flag+=1]")
    kernel1.Evaluate("flag")
    kernel1.WaitForAnswer()
    flag = kernel1.GetInteger()

End Sub
End Class

I do not know why it always give the "Error code: 3. MLGet out of sequence." when it compute the "flag1=kernel1.GetInteger()". and the value of flag1 is always "0". But I search the document of .NETLink API , it shows that we can get the value like this:

kernel1.Evaluate("1+2")
kernel1.WaitForAnswer()
Dim intResult As Integer = kernel1.GetInteger()

So, I just do not know what's wrong with my program.can you give me some help? thank U!