This could be limits on your NGINX config. Do you have this line in your NGINX settings file:
client_max_body_size 5G;
As detailed here: http://forum.mfscripts.com/viewtopic.php?f=20&t=388&p=4583&hilit=nginx#p4551
If that doesn't work try:
client_max_body_size 2G;
Remember to restart Nginx when you make the changes.