Testflight testers getting “unable to download app could not be installed at this time”

Question

I distributed version 1.0, build 1, of my app via TestFlight, and everything worked perfectly.

Yesterday I archived and sent out build 2, and now upon tapping the upd

Answer 1

Bump the build number and resubmit your app. This is a TestFlight/iTunes Connect-side error that, as far as I can tell, we can do nothing about.

Update 12/7: The bug I filed on this (rdar://23296795) was recently returned to me as "We believe this issue has been addressed through changes on our side." – So if you're still seeing this error, please file another radar and let them know it's still not working.

Update 12/10: According to Remy in the comments below, it is still not fixed.