Please see http://www.couchbase.com/issues/browse/NCBC-247 for more info. I’ve recently removed the RestSharp dependency from the core client library. It will be published as an optional, unsigned HTTP client in the May release. The core library will no longer include Hammock or RestSharp references.
The problem is that Couchbase.dll is a signed assembly, and the RestSharp NuGet build is not. The new project structure and HTTP client code is under review - http://review.couchbase.org/#/c/25523/ - and should be published to GitHub soon.