General plugins

I think I'm getting a handle on this problem now. The cron routine loads each module's lib,php file in turn to do it's work. If moodle is running with lots of modules installed there could well be a problem depending on how the cron job runs (and how much memory it's got to play with). I've now reduced the size of the workshop, exercise and dialogue lib.php files. (The "internal" functions used by those modules have now to hived off into their respective locallib.php files.)

Thus if you are not getting emails when you expect them try taking the latest versions of the workshop, exercise and dialogue if you use those modules (from the Modules page once it's updated). If you don't use one or more of these modules and you have an email problem they are best deleted from your site.