This code has been working for some time.

Dim mySFDataAdapter As New SforceDataAdapter(getSFUser, SFConnectString)
Dim mySFDataSet As New DataSet
Dim myRecordCount As Integer = mySFDataAdapter.Fill(mySFDataSet)

Today the Fill method is throwing this exception and failing...

An unhandled exception of type 'System.Net.WebException' occurred in system.data.dll

Additional information: The underlying connection was closed: Could not establish secure channel for SSL/TLS.

I have verified with our network team port 443 is not blocked. What is causing this exception?

Steven