Maybe you are trying to write your first LibreOffice BASIC macro with a simple subroutine call, and you are confused by the error message, "Argument is not optional" like in the picture below:
You should read this error message as "Missing argument in call to function 'Say'".
Probably you have hit the F5-key to run your program, but the cursor was positioned somewhere in the subroutine Say. So LibreOffice (at least version 4.2.3.3) has started your program by calling the subroutine Say without any arguments.
To get it right, place the cursor somewhere into the subroutine Main, and hit the F5-key again. Now the subroutine Main is called on program start, where no arguments are needed, and the subroutine Say is called from Main with the proper argument.