Please disregard my previous question. I found the cause of my issue.
Here are more details in case they help anyone else. When I edited a file in PayPal module using Emacs, Emacs created a backup file with ~ at the end (e.g., incontextvalidate.php~). I believe TB sees this new file as a new page and adds it to table tb_meta. Later, when I click on Preferences > Themes > Advanced Settings, Panda loads the pages but TB fails on validating incontextvalidate.php~ as a valid file name (due to the ~ character). To fix this, I needed to remove the backup file and remove that corresponding record in table tb_meta.