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unable to open some zip files

Aug 6, 2009 at 10:58 AM
Edited Aug 6, 2009 at 11:10 AM

Hi Cheeso,

I'm using your dll (Ver  in an application I'm working on, I’m unable to unzip some files using the dll, the file will not open with either my application or your DotNetZip-WinFormsTool although the files can be unzipped with winzip and winRaR.

Unfortunately the zipped file is subject to copyright as it is a karaoke file consisting of mp3 and a graphics files, placing it on a public forum would be in breach of copyright law, I have mailed you directly of one of the files.



Aug 6, 2009 at 2:26 PM

Thanks for using the forums.

I looked at the file you sent.  It is compressed with DEFLATE64, which is a proprietary compression format, defined but not documented by PKWARE.  It has limited advantages as far as I know, oevr DEFLATE, which is supported very widely.

So, no, DotNetZip cannot open or read that zip file.


Aug 6, 2009 at 3:40 PM

The exception I get is:

exception: Ionic.Zip.ZipException: Cannot extract ---> System.ArgumentException: Unsupported Compression method (0x09)
   at Ionic.Zip.ZipEntry.ValidateCompression() in c:\dinoch\dev\dotnet\zip\DotNetZip\Zip Partial DLL\ZipEntry.cs:line 2903


Aug 6, 2009 at 8:06 PM
Edited Aug 6, 2009 at 8:07 PM

I've changed that exception to:

exception: Ionic.Zip.ZipException: Entry FileNameHere.txt  uses an unsupported compression method (0x09, DEFLATE64)
Jan 26, 2011 at 2:44 AM
Edited Jan 26, 2011 at 8:33 PM

Disregard my comments below. Apperantly Windows 7 uses deflate64 for large files by default and Winzip 9 displays Deflate64 as "Deflate (enhanced)".. The exception message is accurate.


Actually I can confirm, this is bug in the code. I get the same error "Entry XXXX uses an unsupported compression method (0X09, DEFLATE64)" . Here is the replication steps:

1. Compress a large file (3 GB) using Windows .. I am using Windows 7
2. Open it with Winzip  (I have Winzip 9)
3. Encrypt it using AES256.
4. Confirm compression method is Deflate from Winzip>File>Properties
5. Try to unzip it with Ionic.Zip  ... You will get the message above even though compression is not Deflate64 and these exact steps do not cause an exception in small files.

Nov 8, 2011 at 1:19 PM

Hi, i experienced this issue today on a file compressed by WinZip v9 SR-01 using the Compression value of Maximum (enhanced deflate)

This was using version extracting via

testing the zip returned the exception above however testing the archive under 7zip the archive was without error and of course winzip can deal with it.

1) has the library been update to support this compression method?

2) if not is there any plans to? would be useful....

Many thanks




Nov 9, 2011 at 2:20 PM

NO.  DotNetZip still does not support WinZip's proprietary compression methods.

I have no plans to build that. If someone else would like to contribute code that does the work, along with tests verifying that code, I'll consider integrating it into DotNetZip.

Nov 9, 2011 at 8:09 PM

Ok, thanks for the reply, and thanks for the great library!