Roll a ball tutorial error-2 Moving the Player

while I m doing tutorial Roll a ball- Moving the Player . the error occur- Could not load project 'Roll a ball.csproj' with unknown item type '{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}' whenever I try to open C# Script error happen like above. can you solve this problem? sorry for my english . Im not a native english speaker. good luck.