Problem with .NET - substitution group membership not allowed

In the attached set of files .NET objects with "'http://..../SimpleConcept:NetIncome' cannot be a member of substitution group with head element 'http://www.xbrl.org/2003/instance:item" at line 14 in SimpleConcept.xsd

No other validator I have tried gives the same (or any) error and I can't for the life of me figure out what might be the problem (nor can a whole host of other very smart XML knowledgeable folks around the world that have looked at this)

Could someone please confirm what is wrong or what is right please (and tell me how to fix it!!)

Many thanks

Hugh Wallis

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