I finally manage to find out what goes wrong.
It appears to be some bug happened when you try to use a variable with the convert option in the variable pulldown menu in a 'Run FSM'.
Would it be fixed soon? Because it greatly hurdle how we could use template to streamline our production, which is one of the great features of playmaker.
Sorry to bring up this post again.
I stumbled upon a very similar situation again.
When using a variable with the convert option in the output session of a "Run fsm", it gives the " InvalidCastException: Specified cast is not valid." warning again.
But using convert variable in input works just fine.
Would it be fixed in future updated as well?
Thank you.