There are two likely possibilities here:
In Avid, Quickture requires you to export the AAF and WAV files from a sequence. If you try to export AAF and WAV directly from a group or clip, you'll get stuck at the uploading screen. It's not really an uploading issue, just an issue with processing the AAF generated this way.
Your port settings are not open to Quickture servers. Check the link below to make sure the necessary ports are open.
Required Open Ports
Network settings required by Quickture client