Can you create a brand new project, and will it reopen ok?
Chances are something in your game in incompatible with the upgraded software.
You may need to create a new project, then migrate all of your data, one at a time into the new project.
Copy all of your custom/imported resources over 1st (Audio & Graphics folders)
Then, one at a time, copy over the .rxdata files, and test to see if the game loads. (don't save it)
I would do them in database order (Actors, Classes, ...... System last). then the map files.
If one of the files causes an error or freeze-up, replace it with a default file from a fresh project, then continue.
You'll only have to recreate the file (database page) that causes a problem.
This may sound like a silly question, but it has to be asked....
You didn't have RMXP running when you did the upgrade, did you?
Let us know if you still have trouble.
Be Well