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Please, make sure that you have referenced all the new assemblies in your project. In version 5.1, we decoupled the modules and they are in separate assemblies. Double check if you have everything referenced:Upgrading your Sitefinity 5.0 project to the latest version
Do you want to have your say in the Sitefinity development roadmap? Do you want to know when a feature you requested is added or when a bug fixed? Explore the Telerik Public Issue Tracking
system and vote to affect the priority of the items