The .swf flash file is unable to load accordingly even the extension has been included in 'ignoreext' parameter. The issue seems to be browser dependant as the file failed to load in IE 6 only with webagent enabled.
Disabling the ACO parameter - ExpireForProxy resolved the issue. When the ExpireForProxy parameter is enabled, the Web Agent inserts an Expires or Cache-control header into the HTTP response. It prevents caching of content (pages and potentially headers/cookies) by a (forward) proxy server.
It tells the proxy not to cache the pages (ExpireForProxy=yes), the Web Agent adds an Expires header for the page. This header is set to a date in the past, which prevents the page from being cached by a proxy, as dictated by the HTTP 1.0 specification. On 302 redirects, a cache-control: no-cache header is set instead. Although this prevents caching of content, this has the negative consequence of affecting the browsing experience for an Internet
Explorer (IE) browser, as described by Microsoft Support http://support.microsoft.com/default.aspx?scid=kb;en-us;Q297822.