Business event cannot be changed; development plans exist

What causes this issue?

You cannot change the business event in the past because there are
development plans associated with it.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

Delete the development plan item from the individual development plan of
the attendees booked for the event. After this, you will be able to
change the business event.
When you have done this, check the individual development plan of the
attendees booked for the event.
Caution: If the development plan item already has current data in it,
this data is from Training and Event Management (see the documentation
for the switch DPLAN SIMU in table T77S0; note 588403).
If you need a 049 relationship in addition, you must create this again.

Error message extract from SAP system. Copyright SAP SE.