Thankfully, the 20% error that was causing us problems earlier today has been solved. If you received this error, you need to downgrade your version of iTunes.
I decided to downgrade to iTunes 12.1.0 as suggested by several of my Twitter followers, and just like that, it worked. If you're having problems with TaiG 2.0.0 hanging at 20% completion for the iOS 8.3 jailbreak, then try downgrading your version of iTunes.