Civi 4.7.11 Update on Joomla 3.62 with receipts
-- I wanted to thank Brian S for tracking this down and hopefully he will post the fix to the core team.

It was a bug in core as a result of a recent change. The code was looking for the payment processor ID associated with the contribution. But if you have an offline contrib, there is no transaction ID or processor, and the query to do the lookup was triggering a fatal error if the value was null.