I have the same problem, I am using "Application.dataPath/StreamingAssets/T_GameReset.txt" to find the file.
I tried also "/StreamingAssets/T_GameReset.txt" but of course it points then to "C:/StreamingAssets/T_GameReset.txt" and it's not ok.
I want to make this once and for all to be sure it will work on Mac, Linux, and if I'll manage to port the game, also on PS4 and Xbox.
However, it seems I am having problems in general with some actions.
This one, like the other actions I took from the EcoSystem, seems to not complete the state.
It doesn't throw an error, it simply doesn't start any transitions.
I am using PlayMaker 1.8.0.f43 on Unity 5.4.0b17.
Edit: I've just made a test and put the file in C: and this way it works... so I guess there's some problem in catching the error... but I need to know how to point at StreamingAssets.