From a support forum:
I was getting this error when trying to ngen my assembly (.Net Framework 3.5 SP1). In my code I was using a COM Component. I have copied the code from the Interop-Dll, which I have generated about the Visual Studio Wizard, into my project. The following Attribute on my COM Interface prevented to ngen my dll:
[MethodImpl(MethodImplOptions::InternalCall, MethodCodeType = MethodCodeType::Runtime)]
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