Rapid Development 7.7 Error Has not been executed concurrent execution

Hi Mendix Community.  I am taking the rapid Development online class I’m on 7.7 and I keep getting  this error “Microflow 'JimmyFirstModule.ACO_ADE_Registration_SetTotalNumberOfRegistrations' has not been executed, as it does not allow concurrent execution.”   The exercise is to show the count number of register attendee    Thanks for your help!         
1 answers

There are a few things going wrong

  1. [Red circles] You do commit the input/context object in a after commit event of the same object. Thus you create an infinite loop of commits. 
  2. [Purple circle] You are retrieving the wrong object. you should retrieve the training event of the registration
  3. [Green square] You are changing (and committing) the wrong object. this should be the retrieved TrainingEvent (Purple circle issue)
  4. [Yellow square] You return a integer value; which make no sense as it is an after commit event handler

Good luck!