Forum Moderators: Robert Charlton & goodroi
So yes, if your server is incorrectly replying to googlebot's If-Modified-Since header, then googlebot is not getting anything to index. Also possible (but I would think extremely rare) googlebot is sending a bad date or time for the If-Modified-Since.
The solution? I'd make a small change to the page so that it IS now modified, and then also make sure the server is handling If-Modified-Since properly. Check the time/date setting on the server first.