missing file: despite copy of render added to project

[wynwyn]

hi...a bit of guidance appreciated.
i'm looking into the reaper guide but haven't solved this problem.
I render a project to a stereo file.
output is to a folder used for stereo tracks i do other things with....i also tick the box 'send copy to project' (which mostly happens, but sometimes doesn't?)
anyway.....
when i delete the file from my other folder after i've finished with it...the copy in the project is also unavailable?
the 'other' folder is under the general directory 'Reaper'

any help is appreciated
regards

[Philbo King]

After rendering do a Save As, with the Copy Files to project checked. This should create a copy of the rendered file in the project folder that Reaper can use when you reload the project.