The geometry engine for 2.16 utilizes a new libg which is has not yet been released publicly; this engine was put into place to allow some nice new geometry tools, but it requires an update to the core nodes. Look for a Revit (or similar core product) release in the coming months which will provide the necessary dependancy.
I ran into this as well, with a graph created in 2.15.0 sandbox. Looks like in 2.16.0 the LibG.ProtoInterface.dll file used in 2.15.0 (and earlier) has been renamed to LibG.Interface.dll. (That is my best guess, anyway.) I thought I would go ahead and just add the geometry nodes from 2.16.0, but those throw the same error message, even in a new graph.
I threw caution to the wind and renamed LibG.Interface.dll in the 2.16.0 files. That resulted in an unhandled exception, reminding me that throwing caution to the winds often has bad results.