Please help!

I upgraded Designer from 1.2.2 to 1.2.3 today and now when I export I get this message:

layout.setContainer is not a function
Other users have reported this in the Help and Discussion forum also.

Please help, this has totally stopped me being able to work on my 10 month old project, the most basic elements of Designer are broken.

I'm desperate for a fix for this ASAP (like 4 hours ago would be awesome! But I'm guessing it's going to be weeks/months/if ever before this gets addressed.)