Project won't load anymore

I literally got help on this project about a day ago. Now the project stopped working.

It says 'Failed to open project'

(tried again different message: Failed to open project. Check if it is a valid Construct 3 single-file (.c3p) project.)

I've tried: Refreshing the page, and logging out and in, and checking the file to make sure it didn't turn into 0 bytes.

It takes 5.6 MB

so what can I do?

If you refer to this project it works fine: construct.net/en/forum/construct-3/general-discussion-7/help-project-wont-open-anymore-173280

Press F12 and read the console log when you try to open.