code signature not valid for use i… | Apple Developer Forums

I can run my app in the Simulator just fine, but when I try to run it on a device, it chokes with:

dyld: Library not loaded: @rpath/MyF.framework/MyF
  Referenced from: /private/var/containers/Bundle/Application/48637C68-CE05-4B9A-BC3B-EC85295707B8/My.app/My
  Reason: no suitable image found.  Did find:
  /private/var/containers/Bundle/Application/48637C68-CE05-4B9A-BC3B-EC85295707B8/My.app/Frameworks/MyF.framework/MyF

It’s set to Embed and Sign my framework, but it doesn't like the signature. What am I doing wrong? The CodeSign step in the Xcode build seems to go off without any errors.

code signature not valid for use in process