Column argument cannot be null, Parameter name: column from Relations.Add

Hello,

I'm developing a C#, Visual Studio 2015 Pro Windows Form program with a master/detail DataGridView in a SplitContainer.

When I execute this Relation.Add in a Try/Catch:

data.Relations.Add(dataGroups[dgIndex].dataRelationName, data.Tables[1].Columns[dataGroups[dgIndex].parentColumnName], data.Tables[0].Columns[dataGroups[dgIndex].childColumnName], false);

It catches the following error:

This is the SQL statement that it is using to extract the data from the tables:

"select * From Category", "select * From Product_Category_Mapping"

That same SQL Statement works fine in a SQL Server Management Studio Query.

I can't figure out how to resolve it.  I have tried Google searches and MSDN searches.  I have about six other table extracts for other tables that work without a problem using the same code.

Does anyone know what could possibly be wrong with this relation?

Thanks,
Tony

Stop The World, I want To Get Off! ........... Life Isn't About Waiting For The Storm To Pass ... It's About Learning To Dance In The Rain.