"Access denied" error on 'rename' call when uploading files in Symfony

I've been running into the same exact issue recently. I don't really have a good sense of why the problem is happening, but the problem is coming from a step in the process where Doctrine is trying to generate proxy classes.

In my config.yml file, under the ORM section of the Doctrine configuration, I changed the value of auto_generate_proxy_classes from %kernel.debug% to false. I've played with it for a while since making the change and haven't been able to reproduce the issue since.

Found this while looking for same answer, it seems to be a windows + Doctrine issue.

Doctrine Ticket with more detailed info

TLDR: Basically the proxy is trying to rename a file that's still being used, works in Linux but not always on windows.

Go to the file that renames the file, then replace it with a windows compatible rename function

private function renameWindowsCompatible($oldfile,$newfile) {    try {        rename($oldfile,$newfile);    } catch(\Exception $e) {        if (copy($oldfile,$newfile)) {            unlink($oldfile);            return TRUE;        }        return FALSE;    }    return TRUE;}