Getting basic values from contact form using EWS

Using Exchange Server 2010 and progrmming VB.net.

I am trying to get values from an exchange search through EWS. I have managed to get values from my extended userproperties in Outlook contacts with this:

• Dim USER_iban As New ExtendedPropertyDefinition(DefaultExtendedPropertySet.PublicStrings, "iban", MapiPropertyType.String)
• view.PropertySet = New PropertySet(BasePropertySet.FirstClassProperties, New PropertyDefinitionBase() {USER_cprnr, USER_Type, USER_BS})
• Dim foundItems As FindItemsResults(Of Item) = service.FindItems(correctfolder.Id, searchFilter, view)

Works just great. But I am unable retrieve values from fields not in the set of firstclassproperties - like ContactSchema.Birtday.

I have tried with

• view.PropertySet = New PropertySet(BasePropertySet.FirstClassProperties, New PropertyDefinitionBase() {USER_cprnr, USER_Type, USER_BS, ContactSchema.Birthday})

or

• view.PropertySet.Add(ContactSchema.Birthday)

but all the time I get this kind of error: {"This property was requested, but it wasn't returned by the server."}

Are you able to point me in a direction to find a solution?

 - Allan