New Lightroom Masking tool stopped working

[defaultpv4h4eddvc4u]

The new lightroom masking tool has stopped working.  Does anyone know how to fix this?

[Rob_Cullen]

Please include the following in your question:
Adobe product and Version number. A Screenshot of the info panel from MENU: Help/System Info...
Operating system and Version number
The full text of any Error Message(s)
What you were doing when the problem occurred
Screenshots of the problem.

What does "Stopped working" mean?