I found a probable solution here (Reinstalling OWA in IIS6.0)
http://support.microsoft.com/kb/883380
And more information here...
http://blogs.msdn.com/sudeepg/archive/2007/09/11/iis-not-serving-pages-page-cannot-be-displayed.aspx
- But it did not helped - rebooting the server is my only solution yet.
The error I get when calling the OWA URL is : (which is IIS 6.0 related)
Connection to xxx.xxx.xxx.xxx was interrupted while loading the page.
Is reinstalling IIS the only left solution / alternative ?