If 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 in 1.9.1.8 official download doesn’t work correctly, since it tries to get IBM437 Encoding (as ...