I managed to find a blog post on the subject, which links off to an open source project that implements RestSharp. Hopefully of some help to you.
http://dkdevelopment.net/2010/05/18/dropbox-api-and-restsharp-for-a-c-developer/ The blog post is a 2 parter, and the project is here: https://github.com/dkarzon/DropNet
It might help if you had a full example of what wasn't working. It's difficult to get context on how the client was set up if you don't provide the code.