If you encounter the above message when start the PhotoPDF, check the following to resolve the problem.
1. Ensure only single instance of PhotoPDF is running.
2. Follows the instruction shown on the dialog and remove the "*.lck" file. After that, start the PhotoPDF again.
3. To avoid the database locked, please close the PhotoPDF nicely.
4. If problem stills exists, please contacts the PhotoPDF Support Team.