在asp.net中LinkBut​​ton postbackurl错误

Question

我想通过点击Asp.net中的LinkButton通过yahoo messenger发送消息。有时它有效，有时我会收到这个错误：Windows can not access the spesified device, path or file. You may not have appropriate permission to access this item还有Error: Sys.WebForms.PageRequestManagerServerErrorException: An unknown error occurred while processing the request on the server. The status code returned from the server was: 400这是我在VB中的代码，它有什么问题？

Protected Sub LinkButton2_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles LinkButton2.Click
    Dim idname As String = "YMID"
    Dim message As String = "Hello, This is my YM message"
    Dim sendim As String = String.Format("ymsgr:SendIM?{0}&m={1}", idname, message)
    LinkButton2.PostBackUrl = (sendim)
End Sub