You have to ensure that the zip that you upload should have the exe and all the dlls required for the WebJob to run. It seems like you are missing the JSON.NET dll when uploading the zip.
Please ensure you do the following. Select all of the files in the folder, right-click the selected files, and click Send to -- Compressed Folder.
Please follow this article http://www.asp.net/aspnet/overview/developing-apps-with-windows-azure/getting-started-with-windows-azure-webjobs