1.0.0.621: ModBuddy upload "Failed with code - UnknownError"

I'm trying to upload a new mod to the mod browser using ModBuddy. I select the package, it passes all the checks, so I advance to the next screen, where it fails to upload, reporting the message "Failed with code - UnknownError". See attached screenshot.

I tried this 3x in a row with the same results. Then waited half an hour, tried again, same problem. This is my first attempt to upload this particular mod. But I'm a fairly seasoned modder, and have uploaded 3 different mods previously without any issues using the account. I don't think there is anything wrong with the mod itself, as I've had people beta-testing it here for a week and this version doesn't change the functionality at all. I was able to load a game normally with this new mod version enabled.

I have no idea what to try and fix, since I have no clue as to why it's failing. Anybody else had this happen?

With Thalassicus' help, I was finally able to get my mod uploaded, but this is definitely a bug. It turns out that if your mod description is fairly close to the limit of 1024 characters, it can trigger this error. I had it happen at a length of 996. Then I cut it further, to 963, and it uploaded!

See http://forums.civfanatics.com/showpost.php?p=9928268&postcount=15 for a cheap way to save some description length by removing the useless control-return & line-feed characters.