Hi,
you have likely updated Unity version. In some cases, Unity gets mixed up, and so you need to clean up the duplicates, the easiest way is to remove the PlayMaker folder ( careful not to delete templates or globals as they are by default saved inside the PlayMaker folder) and reinstall PlayMaker.
you'll need to manually install it, after you have imported PlayMaker from the Asset store, you'll need to import the package in PlayMaker/Editor/Install
Back up first before doing so.
Bye,
Jean