By using version tags, you can force the browser to make a new request for a cab file when you want to force the client to upgrade. However, depending on how a proxy server is configured, a proxy server may cache a copy of the cab file you are requesting. The proxy server may not respect the version attribute; in this situation the proxy server will return its own cached copy of the file regardless of the browser request for a higher version.

This problem could manifest as an inability to force a client-upgrade despite confidence that you have followed all of the steps described for Upgrading XFile on the Client

To set the content-expiration HTTP Header to "Expire Immediately" on the XFile cab file, do the following:

1. Open the IIS console.
2. Locate the XFile cab file.
3. Right-click on the cab file, choose "Properties".
4. On the "HTTP Headers" tab, check "Enable Content Expiration" then check "Expire Immediately"

What can be done to assist a client-side upgrade when the proxy has already cached a copy of the cab?

Changing the content-expiration setting on the cab file will not clear an already-cached copy off of the proxy server. If you are in this situation, you may have remote clients that need to upgrade, but cannot while they are still receiving a cached copy of the cab file. Some possible solutions to this scenario include:

• Provide your XFile webpage and XFile cab file from an alternate URL. After the user is able to get the correct cab file, you can redirect them back into your existing web application.
• Request that the client-user speak to their network administrator about clearing the cab file from the proxy server cache. Each proxy server is different in how this may be done, and what kinds of other problems it may or may not create.