Using GZipStream (System.IO.Compression) in Unity3d

Hello. I’m trying to use GZipStream in Unity3d. I’ve create project, where I’m using GZipStream (VS 2010, project .net version 3.5, Unity 3.5.6), compile as library, copy to Assets/ExternalLibraries. Everything works, but when GZipStream is ctreating, exception occurs.

System.DllNotFoundException: MonoPosixHelper
at (wrapper managed-to-native) System.IO.Compression.DeflateStream:CreateZStream (System.IO.Compression.CompressionMode,bool,System.IO.Compression.DeflateStream/UnmanagedReadOrWrite,intptr)
at System.IO.Compression.DeflateStream…ctor (System.IO.Stream compressedStream, CompressionMode mode, Boolean leaveOpen, Boolean gzip) [0x00000] in :0
at (wrapper remoting-invoke-with-check) System.IO.Compression.DeflateStream:.ctor (System.IO.Stream,System.IO.Compression.CompressionMode,bool,bool)
at System.IO.Compression.GZipStream…ctor (System.IO.Stream compressedStream, CompressionMode mode, Boolean leaveOpen) [0x00000] in :0
at System.IO.Compression.GZipStream…ctor (System.IO.Stream compressedStream, CompressionMode mode) [0x00000] in :0
at (wrapper remoting-invoke-with-check) System.IO.Compression.GZipStream:.ctor (System.IO.Stream,System.IO.Compression.CompressionMode)
at …

I have the same issue, do NOT know why

Nov 24 2015 Problem resurfaced