My solution for this was to use the code in the Domino Web Access red book which shows how to reset the cache.
basically do the following at the server:
tell http quit
dbc f
load http
This will refresh the cache. dbc f refreshes the cache.
Domino web access is very optimised and this message comes up when the caching has got in a muddle or when someone is changing the Forms6.nsf database.
Details on how to set up an anti virus and spam program.