Can't edit my Animation Events or add new

I've successfully created several animation events inside my animations using sendEvent (string), but suddenly I am not able to edit them or add new. Unity just gives me a "Function not supported" or a "No function selected" dropdown with no events in it.

The sendEvents I already created fire perfectly still, but I can't change them and I can't add new ones.

It should be mentioned that I enter the events manually using the "Add event" button in the Animation window AND that I use PlayMaker, not C#.

Please give me a clue what is wrong here. Thanks.