Solution by Event Log Doctor

I get this error on a few machines after installing the Microsoft Network Monitor 3.1, though the application itself seemed to work OK despite the message (well as good as it works in the first place :-) ).

This is how MS explains the desktop heap:

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Every desktop object on the system has a desktop heap associated with it. The desktop object uses the heap to store menus, hooks, strings, and windows. The system allocates desktop heap from a system-wide 48-MB buffer. In addition to desktop heaps, printer, and font drivers also use this buffer.

Desktops are associated with window stations. A window station can contain zero or more desktops. The size of the desktop heap allocated for a desktop associated with a window station can be changed in the following registry value.
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See the additional link for more information and how to increase the heap if that were necessary.