I was working on my project yesterday morning, and when I come back from work and I open it again, it randomly shows an error message when I open the project.
Failed to open map file. This is most likely because the map was saved with a newer version of the engine.
But I always used 4.9 for that project 
When I open the project everything work except that the map doesnt load, I have all blueprint except the Level Blueprint and the map
Any tip?
Hi Sanwukos,
See if you have a backup of that map file.
\Documents\Unreal Projects\YOUR_PROJECT_NAME\Saved
Let me know if that helps.
Thank you so much, I managed to find a working umap backup, out of them all, only 1 worked.
I created a new map using the latest engine and imported back all and reconnecting missing nodes and im relieved as holy molly xD
Thank you so much !!! 
I just saved days of work.
Great! Iām glad you found a working version!
You may want to think about adding source control software to your workflow (Perforce, etc).