We use specific version of Open Access - 2010.2.1013 which is a custom build. If you have custom modules you need to reference Open Access shipped with Sitefinity, otherwise some problems might appear and you might not be able to process compiled assemblies to add persistence capability.
After the official release we will update the OA version and try to synchronize it with the OA regular builds.
If you install Sitefinity's SDK you can use our Open Access version - 2010.2.1013 and you should get all needed reference in Visual Studio.
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