Visual Studio reproducible error but how to fix it? "already a command handler"

I can reproduce this error by dropping a context menu on my form and editing its items using the built-in dialog. But I don't know what's causing it or how to fix it.

The project has been in production for a year, and now three months' worth of enhancements cannot be put into production because I am unable to add a context menu to the form with the designer barfing:

There is already a command handler for the menu command '5efc7975-14bc-11cf-9b2b-00aa00573819 : 17'

Visual Studio 2005
Version 8.0.50727.762 (SP .050727-7600)

Is there a service pack that fixes this error?