Why won’t the Magic Launcher let me log in?

I have a Dell Latitude D630 running Windows 7 Home Premium 32-but, which I will soon upgrade in various ways so I can run a few classic virtual machines. I also have an Acer Nitro that had been running Windows 10 but it isn’t working right now so I have no choice but to use the Dell laptop.

So I was about to start using it to play Minecraft 1.7.2, but I couldn’t get the regular launcher to work so I tried downloading the Magic Launcher since I usually play Minecraft modded anyway. But the Magic Launcher won’t even let me log in.

Every time I try it just keeps telling me that either my username or password are wrong…and no, I have no problem at all logging into my account on the Mojang website. How can I resolve this?