Before we get into trying to diagnose the problem with that relationship, we should discuss what your goal is. It is unlikely that you need a simple relationship where one event has many employees.
It is more likely that one event has many employee attendees, and also one employee has many employee attendees. In other words you probably have a situation where one event has many employees attending but also one employee overtime may attend any events. Is that your situation?
If that is the case then what you have is a classic many to many relationship. So what you will need is to create a middle table or also called a joint table which is called say event attendees.
One event will have many event attendees, and one employee will have many event attendees.