Back to square one. Could you please check a few more things for me ?
1) Look in the autosave directory, there should be a png for each rendered attempt. Are the previous rendered attempts all 4kb each ?
3.19 kB, actually -- all 800x600 solid black PNG files.
2) Start the program and hit the Retrace button. This renders what is present in the cache directory. Same result as before ?
Yes.
3) Click edit on the lo-res.scene file. This should open up the file in notepad or similar text editor.
Change row 38 from:
background_solid_color 0,0,0,1 //color used if background_type is solid (RGBA)
to:
background_solid_color 1,0,0,1 //color used if background_type is solid (RGBA)
Just change the first zero to a one.
Save the file overwriting the old lo-res.scene file.
Hit the Retrace button again.
This should cause the background to be rendered in red instead of black.
Is if the resulting image all red now ?
Yes.