Hi, and sorry for the delayed reply (forum notifications got messed up and didn't reach me).
If the DOTweenPath is inactive, it means the tween hasn't been created yet, so the Goto will fail. If you don't want the tween to start automatically, just uncheck AutoPlay on the behaviour without deactivating it. Then Goto will work.
On a secondary note, I'm working on a similar project that uses a path with panning touches. Instead of Goto, I'm simply changing the tween's timeScale depending on the pan power.
Cheers,
Daniele