That sounds definitely like a corrupted catalog. We have a default catalog on our website here: http://www.cadsoft.com/faqs.php
that you can download. Scroll near the bottom of that page to find it and download it.
What corrupts a catalog? When Envisioneer is shutting down it goes through a process of saving your catalog with any changes you may have made on the fly. If you shut down your computer during Envisioneer's shut down process, you interrupt that saving process and corrupt your catalog. Always let Envisioneer shut down completely before shutting off your computer.
I also highly, highly recommend saving a copy of your .bdb file (your catalog file) if you customize it. So you can always reload it if you have an issue.