Both Mac and Windows and Dropbox

I use Scrivener on Mac and Windows and have just moved files to Dropbox. Now I run into a project file that will open in the Mac but not Windows. The message I get on Windows is that the project was created in a newer version of Scrivener and will not open. … to check for updates. I did check for updates in Windows and the message is that I am up to date. So, I can open the project in Mac but not Windows. What to do?

You probably have Scrivener 3 on the Mac. Use the File -> Export -> As Scrivener 2 Project command to convert it to a format that Windows Scrivener can read.

(Or install Scrivener 2.9 on the Mac. Or install the Windows Scrivener 3 public beta.)