In my-testexperience the thinreg.exe from V3.358 and V3.386 are only compatible with packets of the same version.
I.e. one cannot longer register/unregister a packet<V3.386 with Thinreg.exe V3.386.
This is very inconvenient(!) and to my knowledge not docomented anywhere.
Is this a Thinstall-error, a test-error or working as designed???