I am really sorry for the inconvenience!
In that particular case I would suggest that we have failed to resolve the correct overload of Returns.
You could try to make the lambda explicit and hopefully we will be able to resolve it correctly.
As for ignoring errors, in pre Visual Studio 2015 versions, we don't have fine-grained filters for ignoring markers. You can turn off the error reporting for the entire file. If that works for you I suggest you have a look at JustCode Options | Code Analysis | General | Exclude file filters.
Please, have in mind that starting with Visual Studio 2015 we are reworking our warning analysis, we are reworking them to be Roslyn extensions. That way you will be able to ignore them with #pragma or attribute as any other msbuild warning.
If you have other problems or suggestions, please don't hesitate to write back!
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