Clearly, your project is referencing something that doesn't exist, something that seems to be called 'Project'.
SUGGESTIONS:
1) Look at your project in the MSVS Solution Explorer.
Then look at your .sln and .csproj files in Notepad (or your favorite text editor).
See if you can figure out what "Project" is missing (or corrupted) and try to fix it.
2) See if you can go back to a "known good" backup of your project, and try rebuilding that.
3) Failing all else, start from scratch with a brand new project, and manually "Add" the source and resources to recreate your corrupted project.
4) Also look at these links:
PS:
If you've made a bunch of changes since your last "Save", then:
5) See if "File, Save" works on a file-by-file basis
... OR ...
6) If you can't save ANYTHING ...
then kiss your changes goodbye...
and remember to save more often the next time ;)