An add-in component named "{0}" in assembly "{1}" could not be found. This could be due to the following reasons: 1. The ...

An add-in component named "{0}" in assembly "{1}" could not be found. This could be due to the following reasons:

    1. The add-in's Name attribute does not match the name provided in the add-in class's 'AddIn' attribute.
    2. The add-in class is not marked as 'public'.