I found this plug-in was causing problems with other plug-ins that use the cron.
The developer of the other plug-in found the following. I was wondering if this could be improved as it's causing a problem?
They [you] are not using the cron_schedules filter hook correctly. The hook's API is here: http://codex.wordpress.org/Plugin_API/Filter_Reference/cron_schedules . They are entirely replacing the schedules and not appending to it as they should.
I added line #338 to the bp-activity-subscription-digest.php file and added line #2250 to the bp-activity-subscription-functions.php file. Both inside the "buddypress-group-email-subscription" plugin folder.