Hi Nick,

Based on my research, we need to specified the attribute as below.
[ClassInterface(ClassInterfaceType.None)]
public class Excel10EventHelper : IExcelAppEvents10, IDisposable

So that we can guarantee that there is no default interface generate for
Excel10EventHelper class.
You may have a try and let me know the result.

Best regards,

Peter Huang
Microsoft Online Partner Support

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