Hello John,
Your question is about Office extensibility development. The right place should be the Office Automation Newsgroup,
http://www.microsoft.com/communities/newsgroups/en-us/default.aspx?dg=microsoft.public.office.developer.automation&cat=en_US_edd5c8cb-2460-4373-a729-fd2e9a1cc9f1&lang=en&cr=USAs to the problem itself, based on my understanding, the answer is no. The problem is not related to the Office XP PIA. The Marshal class is in the System.Runtime.InteropService namespace. So, you need to import this namespace, otherwise the Marshal class will not be recognized.
C#
using System.Runtime.InteropService;
VB.NET
Import System.Runtime.InteropService
Thanks,
Ji
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