I find solving permission errors by going to the Dains folder and right click on the DAINAPP.exe and Run as Administrator. For some reason, Run as Administrator produces the permission error if run from the Start Menu. No idea why.
Permissions are a minefield. Peoples PC's have so many different setups and its even worse if its a Business or School's PC!
Like Bassquake said, try running the app as Administrator. The location of the file looks like it should work ok.
I see you've targeted a OneDrive location for the mp4. Sometimes using cloud based sources can have a unwanted effects when running programs, but in your case it should be fine as its only the source of the video and your working directory (output) is on your PC. Once ffmpeg has extracted the frames & file information, DainApp shouldn't need to query the source file.
I've tried to load mi mp4 for 8 times and it only appears me permission denied