Why have I been able to upload .vwx files in the recent past to a project and can not do so now with a new project?

In the last week and half I have uploaded two projects, both projects were created in Vectorworks 2015 using .vwx file extension. In the first project, I uploaded several folders with one .vwx file contained in each. These folders uploaded with no problem.

Now in the second project I am being told that the .vwx is not an acceptable file format and uploads repeatedly fail. Even when attempting to upload a file used in the first project!
I have tried both to upload just the file and the file inside a folder.

Is there a size limit? Or any other conditions that must be met?

What is going on here? Has something changed between my first uploads and the second?