CLR_E_FAIL in .Net Micro Framework

While porting a library from .Net 4.5 to .Net Micro Framework 4.2, I had a large number of build failures - mainly the expected errors around generics and LINQ, which are not available in the Micro Framework.

Having worked my way through the obvious failures - IEnumerable<T> to arrays, EventHandler<T> to delegate(object, EventArgs), the compiler was reporting this:

I presumed the Micro Framework was having trouble with the foreach keyword, so changed the code to use a standard for loop. Then I received this error:

It turns out that what the Micro Framework doesn't like is multi-dimensional arrays. Where I had Points defined as Point[,] it needed to be defined as Point[][]. It was easy enough to fix, but a meaningful error message would have saved some of Google's bandwidth.