Comment 1 for bug 1813565

Include in your bug report the log files, which are found in the log directory ~/.cache/rapid-photo-downloader/log. You can open this directory by clicking on the link in the "Report a Problem" dialog window. If possible, please also include the configuration file found in the directory ~/.config/Rapid Photo Downloader/.

Until these steps are taken I'm unable to fully diagnose this problem.

Meanwhile, it is clear that your NAS is incorrectly setup. Files cannot be read from it in strictly read-only mode. You need to fix this.