We had a problem on our Web server: whenever a user tried to download a ZIP file from a SharePoint Services site, or from a normal site, they received an error of this type: "The Compressed (zipped) Folder is invalid or corrupted".
To correct the issue we have used this advice (from http://ziprepairsoftware.blogspot.com/2008/02/problems-with-zip-compression-in-iis.html):
You may face this problem if HTTP compression has been turned on in the Web Sites properties of Microsoft Internet Information Services (IIS) on the SharePoint virtual server. When you download a .ZIP file, IIS may encode the file as GZIP (GNU Zip).
To solve this problem, you need to modify MIME (Multipurpose Internet Mail Extensions) type for the .ZIP file from application/x-zip-compressed to the application/oclet-stream. To modify MIME type, please follow these steps:
- Click on Start, point to Administrative Tools, and then click on Internet Information Services (IIS) Manager.
- Right-click on the server (local computer) tree, where server (local computer) is the name of your IIS server, and then click on Properties.
- Click on MIME Types.
- Scroll down to the registered MIME type list to find the .zip entry.
- Click on the .zip application/x-zip-compressed entry, and then click Edit.
- Modify the MIME type value to application/octet-stream.
- Then Stop and then restart the IIS Admin Service to apply the change to the MIME type.