Looking at the code here, it doesn't look like the actual error message returned from `vbx.CreateHostonlyNet()` (or for any of the `vbx.*` functions) get printed anywhere.  Usually, an external package that is treated as a library will not do its own logging, but will return error messages (optionally with embedded error codes with functions provided that determine the kind of error that it is) and the top-level main program will log the error messages (and either take other action or fail like it is doing here). 

At present, I can't see in this code where the actual `err` message is being logged so that the user gets some indication as to why it failed.