A custom object can be associated to 2 distinct "contact".
SOLVE
I created a custom object "registration" and each instance of this custom object must be associated to 2 distinct contacts, one for the "learner", and one for his manager during the formation.
A custom object can be associated to 2 distinct "contact".
SOLVE
It's hard to know why you're getting this error without more context, like what are the exact association API calls being made.
As long as your custom object definition has a MANY TO MANY relationship between contacts and registrations, you should definitely be able to associate 2 contacts to the same registration. Feel free to post examples of your custom object definition and the association API calls if you need further help.
A custom object can be associated to 2 distinct "contact".
SOLVE
It's hard to know why you're getting this error without more context, like what are the exact association API calls being made.
As long as your custom object definition has a MANY TO MANY relationship between contacts and registrations, you should definitely be able to associate 2 contacts to the same registration. Feel free to post examples of your custom object definition and the association API calls if you need further help.