Cannot Run Minecraft from External Drive

I attempted to install Minecraft onto an external drive as to keep all of my games compartmentalized in the same place-- the computer I'm using isn't exactly very beefy, and I can't help myself when it comes to mods and such.

In any case, with my reasoning explained, I should mention that as soon as I installed the launcher to the appropriate place (a .minecraft folder on my SSD) and went to run the launcher, I got the screen depicted below.