MasterFields "EMERGENCY" problem "No index for Fields """

I've got a simple Access Database with 3 Tables :
- Table Tasks :
                  -RefTask : AutoINcrement
                  -TaskName : String
- Table Events:
                  -RefEvent : AutoIncrement
                  -EventName : String
                  -RefTask : the linked Task (only one Task linked per Event)
- Table Actions:
                  -RefAction : AutoIncrement
                  -ActionName : String
                  -RefEvent : the linked Action (only one Event linked per Action)
Different Events per Task.
Different Actions per Event.

In Delphi5, I created 3 TTable Components pointed on my Database throw an Alias.
And i simply want to build 2 Master/Details Forms :
The first one works fine :
TableEvents : MasterFields is RefTache->RefTache
But the second one bugs at creation :
TableActions : MAsterFields would be RefEvent->RefEvent but Delphi refuses
saying "No index for the fields "RefEvent" "

Could anybody help me ?
I've got to do this for tomorrow !!!!!


Christopher N.