Visual Studio "Could not load file or assembly. Operation is not supported" error in Release mode

Did you download Redmine.Net.Api dll from the web? If yes, then browse to it with Windows Explorer, right click on it and choose properties. There you should click 'Unblock'. It might have been blocked for some reasons.

Found two items related to this one is saying to checking if your file is blocked (with some changed to your app.config) and another with changes to your project file. Hope this helps.

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