I believe this problem is related to the fix for
SAK-20672. If you back out that fix, you will not see this problem.
Peforming an activity that sends email to a person, will fail with the following error, against existing trunk (revision 99536), at least when performed in the US.
2011-10-13 13:30:39,965 WARN http-8080-Processor23 org.sakaiproject.emailtemplateservice.service.impl.EmailTemplateServiceImpl - no template found for: sitemange.notifyAddedParticipant in locale en_US
If you undo the changes for
SAK-20672, then sending email works. This appears because the "getEmailTemplate(...)" is used two different ways by different callers. I am attaching a patch, that seems to work for both SAK-20672 and does not exhibit the problem posted above. I am uncertain if my patch has any other side effects, like the previous patch apparently did.
This could affect other versions of Sakai, I only tested against trunk.