X509 signing error with WSDK

I am having difficulties in getting the WSDK Quick Start sample for X509
signing to work.

When I use the code as it is, the dialog (X509CertificateStoreDialog.cs)
shows the certificates I have correctly.  However, the following line of
code returns a null for the certificate collection.

X509CertificateCollection coll = _store.FindCertificateBySubjectName
(_certList.SelectedItems[0].Text);

I tried to work around this problem by changing the code in AddClient.cs as
follows:

//Commented out the code to call the dialog
//StoreDialog dialog = new StoreDialog(store);
//X509Certificate cert = dialog.SelectCertificate(IntPtr.Zero, "Select
Certificate", "Choose a Certificate below for signing.");
//Added this line to grab the certificate directly
X509Certificate cert = store.Certificates[0] as X509Certificate;

This led me to the infamous "An Invalid Security Token was provided"
error!  I recently downloaded Verisign trial certificate and it is valid
for another 2 months.  I have given access privileges to the ASPNET account
as described in the WSDK documentation.  Is there something I am missing?
I would appreciate any suggestions.

Thanks,

Srini

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