Invalid type expression

One example of code that causes this:

int a=0;
int b=0;

If (a==5 && b==6)  Note capital I on the if
System.out.println("Foo!");

As there isn't a command called If, only if, Java doesn't recognize it. A similar error will occur if you put any command that doesn't exist there. If you're sure the command exists, check your spelling and caps.