>> the above will check on the filesize as the script is running from within the script.
Good idea.

>> So if you see zero size perhaps it's coming because you are re-initialising your code and re-running the part the file is created?
I haven't thought about this. Of course it's possible that multiple users working in the CMS might click at the same time. I'd assume that the Controller handles those but I can't make sure that there is only a single process using that file.

I added your filesize/check as well as I added some "dies" and when I start my test-script in 2 different shells the second one immediately stops

filesize: 9254
retrieve-error:  at ../bin/store.pl line 19.
[download]

I'll adjust out function a little and instead of die I might just let it Debug into an Logfile for now.