https://www.dotnetzone.gr:443/cs/blogs/birbilis/archive/2012/11/25/howto-use-dotnetzip-ionic-zip-library-in-silverlight.aspxIf you want to use the latest DotNetZip library (version 1.9.1.8) with Silverlight, you should get a patched version from http://dotnetzip.codeplex.com/workitem/14049, instead of the official download for Silverlight. It seems the Silverlight build inelCommunityServer 2.1 SP3 (Build: 20423.1)