Problems using VirtualBox to access sites on the net

Background I’ve set up my VirtualBox to access my localhost (OSX) by following instructions similar to this post, using NAT. Everything was great until I started testing the staging site on the net (not my localhost). Most things worked fine, but uploading larger images would just fail in IE. Uploads worked fine on the localhost, but failed on stage, so I initially thought it was a configuration on the staging server webserver.