新增保存时出错

在窗体新增保存数据时

提示：

运行错误‘3022’

由于将在索引、主关键字、或关系中创建重复的值，请求对表的改变没有成功。。。。。。

但检测表中并未有重复的值。。。

代码是COPY教程第5章第3节

Option Compare Database

Private Sub ToolbarFrm_ButtonClick(ByVal Button As Object)
        Select Case Button
               Case "保存"
                     cmd_Save
               Case "关闭"
                     DoCmd.Close
         End Select
End Sub
Private Sub cmd_Save()
Dim rst As DAO.Recordset
If IsNull(Me.gh) Then
          MsgBox "请输入员工工号!", vbCritical, "提示："
          Me.gh.SetFocus
          Exit Sub
End If
If IsNull(Me.xm) Then
          MsgBox "请输入员工姓名!", vbCritical, "提示："
          Me.xm.SetFocus
          Exit Sub
End If
Me.Refresh
If MsgBox("您确认要保存吗?", vbOKCancel + vbInformation, "提示") = vbOK Then
         Set rst = CurrentDb.OpenRecordset("tjlyg", dbOpenDynaset)
         rst.AddNew
         rst("gh") = Me.gh
         rst("xm") = Me.xm
         rst.Update
         rst.Close
        Set rst = Nothing
        '刷新数据
        If IsLoaded("usysfrmMain") Then
               DoCmd.Echo False
               Forms!usysfrmMain!frmChild.SourceObject = "frmyg_child"
               DoCmd.Echo True
        End If
        MsgBox "保存成功!", vbInformation, "提示"
        Me.gh = Null
        Me.xm = Null
End If
End Sub
请求帮助，谢谢