When accessing Communicator Web Access (CWA) on Microsoft Office Communications Server 2007 R2 the following error is shown to the user
Internet Explorer cannot download CWAPlugin.exe from cwa-domain.com.
Internet Explorer was not able to open this Internet site. The requested site is either unavailable or cannot be found. Please try again later.
This error was due a Internet Explorer security configuration on the client side. Adding the site to Trusted site and chainging the security settings for the zone to prompt instead of denying ActiveX components, soved the problem here.