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

Encountered exactly the same problem today, trying to install a new testflight version downloading it through our company WiFi. We noticed that we could still download and install the app from mobile devices through LTE which lead us to the conclusion that for whatever reason testflight must have blocked our office IP (temporarily) for unknown reasons.

I hope this actually works for someone else. I was seeing the same result over and over again. I restarted my phone. I took my account off the Test Flight list and re-invited myself. Same result. 2 other people were able to install, but I wasn't. I furiously tapped "Install" several times as fast as I could, then tapped "Retry" when the alert box came up. Continued to tap "Install" over and over again, then "Retry". Install, Retry, Install, Retry. Then it finally started installing...

I wish I were making this up.

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.