I'm assuming that the person who originally posted here was using Windows Workflow and had defined his Workflow with an XOML file.
I was running into a similar error with a State Machine Workflow: "GetRuntimeValue failed since Path 'xyz' evaluated to 'null' value."
Turns out (after hours of beating my head against the wall), I have a handleExternalEventActivity in which I forgot to assign a value to the 'e' property which basically tells my activity where to find the event arguments. Arghh! Once I assigned
a value to the property all was fine.
Hope this helps someone else with a similar issue.