HowTo: Use DotNetZip (Ionic.Zip) library in Silverlight
If you want to use the latest DotNetZip library (version 22.214.171.124) 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 126.96.36.199 official download doesn’t work correctly, since it tries to get IBM437 Encoding (as the original ZIP spec required) from Silverlight, but that encoding is not available via Encoding.GetEncoding method in Silverlight (neither encoder and decoder fallbacks for GetEncoding are available as in .NET 4.5).
So the patched version uses Unicode encoding instead (only UTF-8 and Unicode [UTF-16] Encodings are available in Silverlight), although it could have also used a text encoding class generator for the missing encoding and change the source code similar to how Mike Taulty had done with an older version of DotNetZip.
I do prefer the Unicode approach, since using the IBM437 codepage would have issues with Unicode filenames. ZIPs with such filenames are supported fine by most modern ZIP viewers, including Windows Explorer’s Compressed Folders views in recent versions of Windows.