Notification emails not sendin

Hi,
I am having issues with notification emails not sending.
All the BP notification emails are sending e.g. mentioning or group invites, but nothing from the plugin, e.g. follow up comments on a forum thread or digests (in fact trying to see queued digests crashes the site). After my last upgrade, it seemed to work briefly – then stop. It is potentially something up with my setup, by I am getting no error logs or php files called.

Here was my thread in the bp forums http://buddypress.org/community/groups/how-to-and-troubleshooting/forum/topic/notification-emails-not-sending-2/

Can you help at all?

Thanks

http://ww.wp.xz.cn/extend/plugins/buddypress-group-email-subscription/