When you try to extract a Zip file that is downloaded from the Microsoft Windows SharePoint Service Library, you might receive the following error message:

“Cannot open file: it does not appear to be a valid archive. If you downloaded this file, try downloading the file again.”

You might experience this problem if the HTTP (Hyper Text Transfer Protocol) compression has been enabled in Web Site’s properties of Microsoft IIS (Internet Information Service) on SharePoint Virtual Server.

Cause
When a Zip file is downloaded using IIS, IIS may encode that file as GZip (GNU Zip). Thus, the browser clients pass that file directly to unzip program. But the program can not read the file and thus shows you this error message.

You may also encounter this problem due to Zip file corruption. The corruption can take place because of incompatible compression standard. The unzip program can not read the file in this case also and thus you get the error message.

Resolution
To fix this issue, you are required to alter the MIME or Multipurpose Internet Mail Extensions type of your Zip file from ‘Application/x-zip-compressed’ to ‘Application/oclet-stream’. MIME type can be changed from the IIS Manager.

If changing the type of MIME does not help, then the problem is due to Zip file corruption and you need to opt for zip recovery software to resolve it. For easy and automated Zip Recovery, you should go for third party utilities, known as Zip Repair software.

Stellar Phoenix Zip Recovery is the most advanced and commanding tool that ensures complete and safe Zip Repair in most of the corruption scenarios. This Zip Recovery tool can repair zip file up to the size of 800 MB.

This Zip Recovery tool is compatible with password protected Zip files of WinZip 8.0 and earlier versions. It can repair sub-types of Zip files till WinZip 11.1 that do not need password for opening. It supports Windows Vista, XP, 2003, 2000, NT and Me.