This message means that something is blocking the upload, especially if the file is larger that 1 GB. A lot of times this is your ISP (internet service provider) like Comcast, Verizon, Charter, etc.
Sometimes it is your antivirus software, but that is more common for downloads.
However, one ISP in particular, HughesNet, seems to block uploads right out of the box even if the file is tiny.
A helpful customer sent in the following steps to resolve the issue:
1) Open up Hughesnet control center.
2) There is a grey bar that says "what do these controls mean?", click on the the little guy symbol next to that.
3) This opens Advanced Configuration and Statistics. On the left side click on Turbo.
4) This opens up 5 submenus, click on "Control". This opens up a submenu called Enable/Reset.
5) Click on that and it will open up a popup box and just click on the radio button thats says Disable.
6) Click Ok.