Outlook 2007 VBA Syntax To Change The Value Of A Contact Property

I have been struggling for three hours trying to find the syntax to change the value of a user-defirned field on a custom contact form.  I am able to read the value of the field with the following syntax:

Dim objNS As Outlook.NameSpace
Dim objContactsFldr As Outlook.Folder
Dim objContactItems As Outlook.Items
Dim objContact As Outlook.ContactItem

Set objNS = Application.GetNamespace("MAPI")
Set objContactsFldr = objNS.GetDefaultFolder(olFolderContacts)
Set objContactItems = objContactsFldr.Items.Restrict("[MessageClass = 'IPM.Contact.LeadGen1_1'")

'This reads perfectly
Debug.Print objContact.UserProperties.Find("CallTask1").Value

'But this fails with Error 242 - Object required ...
Set objContact.UserProperties.Find("CallTask1").Value = True

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I can't figure out what I'm doing wrong.  I can't find anything by Googling.  Is this a black art or something?

Thanks,

Bill Vallance