Why can't I save file in Eclipse Juno?

This is a known issue in Eclipse Juno:

https://bugs.eclipse.org/bugs/show_bug.cgi?id=396418

As a workaround, use 'Save All': Shft+Ctrl+S

Try: Save as. It will tell you what is a problem in your code. Probably you did "copy-paste" and some characters cannot be mapped using "US-ASCII" encoding characters.