It's either a glitch or some aspects of your previous name was on a blacklist of some sort (idk your filename doesn't look like something that would belong on a blacklist)
Apparently the name matched something on the blacklist (MediaWiki:Titleblacklist). How it does I don't know, there doesn't seem to be something like that on there.
I noticed that the system swapped the colon in "ML:SS" for a hyphen when I uploaded it a second time. Perhaps that has something to do with it, but I don't see why it'd give me such a vague error and why it was settled so easily the second time.