Build failed, illegal characers in path.

I’m new to unity and i’m facing a problem.
In the tutorial “Roll A Ball” game when i build the C# code it shows Build failed, illegal characters in path.
I tried so much to remove it but problem isn’t resolved.Due to this ,i’m unable to do anything further in unity. When i hit play and give input nothing happens.
So please help me over this issue.
Thanks in advance.

What platform are you trying to build for? What version of Unity are you using? If building for mobile, which SDK are you using?