If you just uploaded it when trying, give it a bit, if it's still failing, try restarting your game or waiting a bit longer, if that fails, copy the mod into your main mod folder rather than being in data/mod/modmaker. and try again, it should work, if all else fails, then i don't know what's the problem.

also i would like to note make sure you type the name of the mod exactly as it is on the file, and do not put spaces in the mod name.