This fixed the problem. In Quickbooks go to:
File > Utilities > Stop Hosting Multi-User Access and follow the on-screen prompts.
You can then open up a Quickbooks file in a BC container.
For whatever reason, a change from BC 1.3.2 to BC 1.4 (and 1.5) causes Quickbooks Mult-User Access to throw an error message. Turning off this feature fixes the problem.
Mult-User Access is not a feature I need so this is not a problem for me.
(If anyone wants to look further at this issue you should be able to re-create the issue by turning this feature on.)