I have try other levels in the same project. they work fine. I have tried the backup level, but no luck there. I have tried renaming the umap file, Nothing.
I just worked through a problem similar to what you are having. I was able to save most of my umap by loading up a backup. To do so go to Saved->Backup and copy your .umap file. Then go to where your file that is isn’t opening is saved, delete it and paste in the backup in its place. Make sure the backup has the same name as the file you deleted. It won’t restore everything but it at least will keep you from starting from scratch.