Is there a way to use API to encrypt SDL file based termbases?

I would like to periodically encrypt new file-based termbases. There is internal API oTB._Reorganise(bool vb_encypt, bool vb_markReadOnly, int I_expiryDate) that I found but does not seem to work. Seems to throw System.NullRefrenceException every time while oTB.Reorganise() works fine.
For example oTB._Reorganise(true, true, -1);

These are in Sdl.MultiTerm.TMO.Interop.