Error Message:

(if you try to merge a document)

You are trying to read or write to protected memory, this is a sign that the memory is corrupt.

Problem:

The reference is not set correctly.

This is caused by the Security Update for 2007 Microsoft Office System (KB2251419).

Solution:

You have to delete this security update and the merge will work without any problems.

(Tested on XP with Office 2007)