If you are getting errors after importing or having trouble updating to the latest version of PlayMaker using the Package Manager or Asset Store, please check this thread:
https://forum.unity.com/threads/package-manager-not-showing-latest-version-from-asset-store.791718/Basically there are bugs in the Package Manager/Asset Store, and the workaround is to manually delete the downloaded package:
Windows: %APPDATA%\Unity\Asset Store-5.x\PUBLISHER\CATEGORY\PACKAGE.unitypackage
OSX: Library/Unity/Asset Store-5.x/PUBLISHER/CATEGORY/PACKAGE.unitypackage
After deleting the cached package, the Package Manager/Asset Store will download the correct version and you can import it.
NOTE: After importing you can install the latest version of PlayMaker from the Welcome Screen. If the project has errors the Welcome Screen may not be available, in which case you can import the latest version manually:
Main Menu > Assets > Import Package > Custom Package
Assets\PlayMaker\Editor\Install\Playmaker1.9.1.unitypackage
See Also this thread on a related Asset Store bug:
https://hutonggames.com/playmakerforum/index.php?topic=20096.0