在以上程序中的Text1中输入数字，为什么有的数字可以实现加密后解密，有的数字加密后无法解密？
Private Sub Command1_Click()
On Error Resume Next
n = Len(RichTextBox1.Text)
For i = 1 To n
RichTextBox2.SelText = Chr(Asc(Mid(RichTextBox1.Text, i, 1)) Xor Val(Text1.Text))
Next
Text1.Text = ""
RichTextBox1.Text = ""
End Sub
Private Sub Command2_Click()
m = Len(RichTextBox2.Text)
For J = 1 To m
RichTextBox1.SelText = Chr(Asc(Mid(RichTextBox2.Text, J, 1)) Xor Val(Text2.Text))
Next
Text2.Text = ""
RichTextBox2.Text = ""
End Sub
