Today I was creating a custom template for a DataGrid (something I don’t do too often). I created one template and it worked just fine. On my second template I received an error:

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Key can not be null. Parameter name: key

So, I began investigating. Of course the error message doesn’t mean much, so I started looking for things like primary keys in the data base and making sure the db and sproc returned results. Well, the error was actually caused by a misspelling of one of the variables (using C# - argh!). Turns out that was the problem. I’m not sure if anyone will ever run into that error, but if you do, hope this helps!