Well, given that the code in the link is for updating a bookmark, which is what your initial post was apparently trying to do, one shouldn't expect it to work with a custom document property. Have you even looked at any code samples dealing with writing to custom document properties or variables? For example, to add and update :
• Custom Document Properties, see: http://support.microsoft.com/kb/212618/
• Document Variables, see: http://support.microsoft.com/kb/306281/
I can't see how you could think the code you've posted has anything to do with what's in the link, or with updating a custom document property.

I think you need to spend a little time working out how one uses the various methods available for populating a document. When you decide what you want to work with, be that a bookmark, a content control, a custom document property, a table cell, a specified paragraph (via its index #), etc., then stick with code related to that method rather than trying to use code designed for something else.

As for:
That suggests you don't understand what error codes are about...

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]