We discovered a showstopper bug in the most recent version of OpenBoxes (v0.6.3) that occurs on some, but not all instances. If you see an empty category selector (see the screenshot below), please upgrade to the version 0.6.3.1. The bug may prevent a user from creating or updating products, as well as browsing inventory by category.
You can download the v0.6.3.1 release from github:
Here's a screenshot of the bug: