So that the project can open again, with this kind of error in W7 go to organize, folder and search options, view, abilite show hidden files and folders.
Then go to Cakewalk Projects, open the folder that your music and delete the file (cwp.assets) and renicie the computer.
For me it worked, did not lose anything and I can finish my project.
Probably the error was recorded this damn file, and when u open it again create another without the error in question was worth, and rock!
Ps. Uncheck hidden files and folders.