I have been on Gather for over five years now, and I love it, but the site has some issues, and I address them as I see them come up with comments, but now, I will do an article that I hope will help.
Uploading a video: I have found that mostly YouTube videoes work on Gather if you go to embed, and scoot down to the fourth box that says to upload "Old style." They work here on site.
Photos: I can't upload photos off Firefox. I have to use either Google Chrome or Internet Explorer.
Sometimes I have trouble commenting, and then I hit F5, and the page will reload and then, I can comment.
Finally, I always copy my articles before I submit them. It saves them from the dreaded message: oops!
Good luck, and I hope it helps!