A high volume classic ASP page is using an ASP.NET page to return xml data, taking advantage of .NET caching capabilities. The cache being used in the .net page is the Context Cache. Recently after 1 year of running smoothly - IIS7 starts responding with a 503 unavailable and in the HTTP.sys error log it displays a few connection_dropped events, then a slew of connection_dropped_list_full events. At this point the servers is unavailable.
Looking at possibilities of having hit a cache limitation or a network problem.