It seems that the system error message description table is not included in your WinCE.NET 3.92 build for Graphics Master. Here's my request/vote to add it to your standard .NET build. This is the first time I am aware of that it either has been left out or is broken in some way. I've used FormatMessage with many GC+, GM 3.0 builds in the past (it's now returning fail and leaving the buffer empty).
Thanks,
Bruce
From the eVC 4.0 documentation on FormatMessage()...
Not all Windows CEābased devices will contain the system message-table resources. This is a selectable part of the Windows CE operating system and is often removed to conserve space.