Symptoms

A smartform client event was running into an issue where if the email message was customized it would not get sent to the participant (however it would create the task for them in the worklist fine). If left as default, the email sent without issue.
 

Diagnoses

There was only one field used in the custom body and it was not used anywhere else in the workflow and without the server logs it is difficult to say why this causing the client event to fail.
 

Resolution

Since this particular field was not significant to the workflow it could safely be removed and at this point the client event functioned as one would expect.