用户密码都正确就是登陆不了，哪位大神能开出来代码有什么问题？

[cqpph]

Imports System
Imports System.Data
Imports System.Data.SqlClient
Partial Class login
Inherits System.Web.UI.Page
Dim conn As New SqlConnection(ConfigurationManager.AppSettings("datalink"))
Protected Sub linkbtnok_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles linkbtnok.Click
If txtname.Text.Length = 0 Then
alert("登录时用户名不能为空！")
Exit Sub
End If
If txtpwd.Text.Length = 0 Then
alert("登录时用户密码不能为空！")
Exit Sub
End If
Dim cmd As SqlCommand = New SqlCommand("chklogin", conn)
cmd.CommandType = CommandType.StoredProcedure
cmd.Parameters.Add(New SqlParameter("@loginname", SqlDbType.VarChar, 20)).Value = txtname.Text.Trim
cmd.Parameters.Add(New SqlParameter("@loginpwd", SqlDbType.VarChar, 20)).Value = txtpwd.Text
cmd.Parameters.Add(New SqlParameter("@userid", SqlDbType.Int)).Direction = ParameterDirection.Output
Dim userid As Integer
Try
conn.Open()
cmd.ExecuteNonQuery()
userid = cmd.Parameters("@userid").Value
cmd.Dispose()
conn.Close()
Catch ex As Exception
alert(ex.ToString)
End Try
If userid = 0 Then
alert("用户名或密码错误，请重新登录！")
Else
Session("sbly") = "pass"
Session("userid") = userid.ToString
Response.Write("<script language=javascript>window.returnValue=true;window.close();</script>")

End If
End Sub
Sub alert(ByVal msg As String)
Response.Write("<script language='javascript'>alert('" & msg & "')</script>")
End Sub

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
Session("sly") = Nothing
Session("userid") = Nothing
End Sub



End Class