I've had the same issue, havent been able to fix it yet. It also won't open with the ver9.00 production version. I was able to verify the following:

CMPV size 129,311 bytes seems reasonable

CMIX header present.

Embedded ZIP archive present.

Central directory intact.

End-of-directory record intact.

Four screen files present, this matches how many screens I had

Alarm databases present.

7-Zip can enumerate contents.

project file attached

This is a concern with Beta software and one of the reasons we watermarked the projects. As the software was still changing, the project file formats were still being updated. Unfortunately, there are few options to recover that work.

One thing you may be able to try is - using the Beta version that created the project, save your screens to the screen library (right click on the screen thumbnail on the left panel). Also Export your tag list and event manager list. Then in the production version, reimport everything. Depending on where the project format changed, you may be able to reconstruct most of your project.