I realize this thread is pretty old, but I just wanted to add that I just tried upgrading from Toast Titanium, v11 to the new v16 on my Mac Pro running OS X Sierra, and I ran into the same issue. I can only get the application to launch when I do it from a new user account I create, or from my "Administrator" account I normally never use.
Just out of curiosity, I tried removing it and trying Toast, v15 and v14. Had the exact same problem with both of those releases too!
I searched all over the net for solutions to this and came up pretty much empty. The only potential lead I found was someone with a similar issue using Toast, v8 with an older OS X version. In their case, the solution was removing DivX or Xvid codecs that were in a folder under Library for Quicktime components/add-ons. I checked my system though and didn't see a sign of any of these QT add-ons present.