One of the best extensions yet for MainWP is the Favorites Extension.
Its overall very handy so you can keep all of your themes and plugins at your fingertips to put on your sites any time you want.
With that said, today I ran into a problem. I was uploading a few new plugins to my favorites and I was getting 2 different types of upload failed messages.
Solution to Error 1
Filename is too long. Shorten up the name of your Zip file then try to reupload.
Solution to Error 2
In some cases it doesn’t seem to like underscores.
Also, check and see if you need to unzip the file first and the actual plugin is a zip inside a zip.