Hi,
So I assume you have upgraded from 1.x to 5.x right?
Typically, what worked for me was to first update PlayMaker when still in 4.x and then when it all works upgrade the projec to 5.x.
Can you try that?
else, I would try to package scenes and prefabs from your 4.x project and import them into a fresh 5.x project with PlayMaker already installed, basically from a clean project where PlayMaker is properly installed.
get back to me if you have still problems. It's a pain for everyone... Unity evolves and it's a good thing, but it makes updrading from major version something difficult. I would tend to say it's best like that, otherwise Unity would be locked into old ways, so I personnaly prefer they move forward then simply stay stuck because they privilege backward compatibility. But yeah... it means it's a pain to upgrade
Bye,
Jean