-renderproject not working - "ERROR OPENING FILES"

I originally posted this in the main forum thinking I may be missing something, but I could not find a solution. I have tried the -renderproject switch on several different reaper projects with several different settings and on two different computers. And I always get the same error. (tried v2.56 and v2.57) It seems to want to work, but then once the project opens and the render dialog appears....it gives the error: "<<ERROR OPENING FILE(S)>>". And in the "Output file" space at the top it says "No output". I tried setting the default render path. I tried leaving it blank. I tried .wav render and .mp3. All give the same error. However, if I open the projects and go File>Render... everything renders fine. So, it appears to be in the handling during the -renderproject mode.

Maybe you should post the exact command line command you're using!?

yeah, sorry...it was in the other thread C:\Program Files\Reaper\Reaper.exe -renderproject "G:\Folder\mu77.rpp" I also tried the "send to" method detailed by drew

Actually it's not really broken but incomplete programmed:

Put into tracker: