Thank you for reaching out. The error you're encountering might be due to compatibility between the BETA and current versions of Adobe Express, which use different file types. To troubleshoot:
1. Check if the project was created in the BETA version.
2. If yes, try opening it in the same BETA version.
3. If you're using the current version, recreate the project to see if the issue persists.
If the problem continues, log off, clear your cache and cookies, test it in incognito mode or perhaps try updating your browser.
Give it a try, and let me know how it goes, as I'm here to help.