Try
            Dim comstr As String
            If CmbPurview.Text = "一般用户" Then    '判断注册一般用户还是管理员
                If TxtPassword.Text = TxtConfirmPassword.Text Then      '确认密码填写无误
                    comstr = "insert into" & CmbPurview.Text & "values('" & TxtUserName.Text & "','" & CChar(TxtPassword.Text) & "')"
                    '定义一个sqlcommand类实例,并初始化
                    Dim mycom As New SqlCommand(comstr, SqlConnection1)
                    SqlConnection1.Open()
                    mycom.ExecuteNonQuery()     '执行命令
                    SqlConnection1.Close()
                    MsgBox("添加成功!")
                Else
                    MsgBox("两次密码输入不相同!")
                    TxtPassword.Text = ""
                    TxtConfirmPassword.Text = ""
                    TxtPassword.Focus()     '把焦点落在密码的文本框
                End If
            Else
                If TxtPassword.Text = TxtConfirmPassword.Text And TxtSuperPassword.Text = "applehuang" Then
                    comstr = "insert into" & CmbPurview.Text & "valuse('" & TxtUserName.Text & "','" & CChar(TxtPassword.Text) & "')"
                    Dim mycom As New SqlCommand(comstr, SqlConnection1)
                    SqlConnection1.Open()
                    mycom.ExecuteNonQuery()
                    MsgBox("添加成功!")
                Else
                    MsgBox("密码错误!")
                    TxtPassword.Text = ""
                    TxtConfirmPassword.Text = ""
                    TxtSuperPassword.Text = ""
                    TxtPassword.Focus()
                End If
            End If
        Catch ex As Exception
            MsgBox("该用户已经存在,请选另一个用户名!")      '异常处理,如有相同用户名存在就会出错
            TxtUserName.Text = ""
            TxtUserName.Focus()
        Finally
            SqlConnection1.Close()
        End Try

生成没错误,但我点注册新的用户,它总是提示"该用户已经存在,请选另一个用户名"