The requested screen does not exist inside this capsule

unknown

When I create a new screen in a Capsule (not all capsules, just one) I get the message: The requested screen does not exist inside this capsule

The screen is created and can be closed and re-opened (whereby I see the same message again).

Initially thought it might be because I have a Mask with the same name, but this is not the case.

unknown

I think I have solved this issue myself.  I had previously deleted a Mask, but still had screens that had been using this mask and I had not yet assigned a new mask to them.  Once I assigned a new Mask to these screens (even if I then deleted it after a save) the problem went away for me.