This is a known error that is being looked into.

To reproduce:
1) Launch Cubase with plug-in pack enabled KB37 connected, configure Cubase to use KB37 for ASIO I/O.
2) Create a 96/24 session in Cubase.
3) Create an audio track in the session.
4) Instanciate GearBox VST across first insert point of audio track.
5) Save session, quit Cubase.
6) Disconnect KB37 from CPU.
7) Wait 5 seconds, connect TonePort DI to host.
8) Relaunch Cubase.
9) Open saved session.
10) Select TonePort DI for Cubase ASIO I/O.
Result: Error dialog thrown, "(Code 80000000) An unknown error occurred."

We hope to have this error corrected in the next Gearbox update.