This is related to the outline_javascript filter, which is dependent on the cache being reliable and unlikely to evict anything added in the past few seconds.
In this filter, it will take large blocks of inline javascript and turn it into an external resource, writing the inline block as a cache entry. When the javascript file is fetched by a browser, if it's not in the cache there's no way to reconstruct it. This filter can only be used in single-server setups or when using memcached (assuming memcached is large enough that it's unlikely to evict anything quicky).
The message you are seeing is consistent with a multi-server setup, or if your cache implementation not being fully reliable or large enough to hold onto an entry long enough to accommodate the round-trip time from a browser. Simply turning off outline_javascript (and outline_css if you have it) will make these messages go away.
-Josh
-Josh
-Josh