Broken YAML file on controller after import into 5.2.1 - animation does not play

I’ve just updated from Unit 4.6.8 to 5.2.1 and imported my project, and I have import errors on 2 animation controller files of the form:

Broken YAML file(Assets/Animations/FreeStuff.controller). Local file identifier (110242901) doesn't exist!

And, although the blue time bar is updating in the Animator window, the animations on these controllers do not seem to have any effect on the GameObject that they’re supposed to animate.

2314925--156014--Screen Shot 2015-09-28 at 10.43.10.png

Has anyone else seen this, and knows a quick fix?

Repro case submitted. Bug #731537.