by Colin Fraser.
Well, if it is not a setting in IIS Manager, then the only other thing it may be is that there is an AppFrabric cmdlet that is throttling the server. That is of course, if the server is the issue. But reading Matteo's post that suggests a limitation that is just not going to be gotten around programmatically. The throttling was my one shot, as I can't see if anyone else suggested it and it is pretty uncommon these days but it is possible.
I suspect Matteo is correct, then until you change your version of PHP to a 64 bit, you have hit your limit. AFAIK, 2GB is the limit of PHP 32bit simply because the used integer type is signed which limits file sizes to 231-1, ie. 2GB.