memory map compression encryption

Guys,

Is it possible to use the .Net 4 Memory mapping solution with an encrypted/compressed file on disk?  Im having trouble and feel it may not be possible, Ive googled around and there doesnt seem to be a lot on this specific point, heres a test code snippet Ive setup (which compiles) but doesnt run.  Note if I use a filestream and avoid the memory map idea it works properly, In this scenario the accessor is grabbing everything as Im using a small file for demo purpose.  FYI its getting to where the "line = sReader.ReadLine();" before hanging (theres no exception throwing, I have to exit VS2010 to stop it) cheers

 I need a heads up on whether it can be done, and if so how to alter this snippet to work properly, cheers

		private string GetLastDateInFile(string filePath)
			{
			string[] lineString;
			CryptoStream decryptStream;
			C1ZStreamReader compressReader = null;
			string line;
			string[] lastLineString = null;

			// If the file does not exist, return ""
			if (!File.Exists(filePath))
				return "";

			FileInfo fileInfo = new FileInfo(filePath);

			using (MemoryMappedFile memoryMappedFile = MemoryMappedFile.CreateFromFile(filePath, FileMode.Open))
					{
					using (MemoryMappedViewStream accessor = memoryMappedFile.CreateViewStream())
						{
						// open expander stream on compressed source
						decryptStream = new CryptoStream(accessor, Global.DECRYPTOR_MAIN, CryptoStreamMode.Read);
						compressReader = new C1ZStreamReader(decryptStream);

						using (StreamReader sReader = new StreamReader(compressReader))
							{
							line = sReader.ReadLine();

							while ((line = sReader.ReadLine()) != null)
								{
								lineString = line.Split(',');

								if (lineString.Length < 13)
									continue;

								// remember the last
								lastLineString = lineString;
								}
							}
						}
					}

			// return the datestring
			return lastLineString[1];
			}

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