Exactly what version of Movie Edit Pro are you using? Possibly something is blocking the program from accessing the Internet properly (e.g. firewall settings). I guess if it comes down to it, you can always put in the extra step and export the video clip to your hard drive via "Export movie" in the "File" menu and upload the resulting file to YouTube via the upload function on the YouTube website. Use something compatible like WMV or MPEG-2 to export from Movie Edit Pro. YouTube supports a bunch of formats.
I am using Magix Edit Pro 14. It shows mixing down stuff, but strange I don't see the wmv option to convert the file to. I ended up just using movie maker, but I'd love to figure out why this is happening.
I use Video Easy and am working on the same problem.
There is an option under the firewall settings to ADD a program to the "exclusion" list. There you can try adding the program and see if it will upload to YouTube.
However, normally when a program tries to bypass the firewall, an alert pops up. Mine is not doing this though.
I will update you on my progress. Please update on yours.