Have you checked the error message on the File node when it fails with your own vdb file? There's usually a message that explains why it failed, and you should be able to correlate that to the exceptions thrown in openvdb/io/Archive.cc.
Those examples are pretty old though and I suspect wouldn't help you anyways for the problem you're describing. The file loading of vdb files in Houdini is pretty vanilla, the code can be found in the openvdb github repo here:
As a sanity check, you can try loading your own created vdb files using `openvdb::io::Stream` to ensure that there wasn't something else wrong when you created the file.
Cheers,
-Edward