First of all, I want to thank you for your interest in RadRichTextBox.
Now straight to the issue - I tried to reproduce the problem, but to no avail. I've applied Office_Black
theme successfully. Can you delete bin
folders in your solution and then try to rebuild it? If the problem still exists, it will be great if you try to isolate the issue in a sample demo project and send it to us.
Also, can you please share in which theme you are getting an error related to BooleanToVisibilityConverter
Looking forward to your reply.