Scratch

Your firewall may limit the size of data uploaded via an HTTP "POST" request. Try uploading a completely empty project. If that works, then this could be the problem.   If not, adjust your firewall settings.  Certain firewalls can prevent you from uploading your project to the site.  It could also be that you  need to allow direct access to the host "scratch.mit.edu" 
If none of these ideas help, please send us your .sb file and describe the steps you use to share your project.  Please send this to: scratch-try@media.mit.edu

To get help on particular types of security software configurations or to share a solution that works for you, please post to this forum:
http://scratch.mit.edu/forums/viewtopic.php?id=1004&p=1