Sorry I see the same problem, but I don’t expect to release a fix in the near future. Something must have changed in one of the OS updates to break this. I do plan to eventually get back to WriteRoom, but now TaskPaper is taking my time.
In the meantime you should be able to print your documents, you’ll just need to use TextEdit (which is included on all Macs). TextEdit should be able to open and print any WriteRoom document.