When using before_save in SugarCRM 6.5 how do I stop the save?

Try paste this when you need show error:

require_once 'include/api/SugarApiException.php';
throw new SugarApiExceptionInvalidParameter("It can't be done");

A brute way of doing it is:

die("it can't be done.");

Or you can:

SugarApplication::appendErrorMessage('<div style="color:#555; border-radius:10px; font-family:Tahoma,Geneva,Arial,sans-serif;font-size:11px; padding:10px 10px 10px 36px; margin:10px; border:1px solid #f5aca6; background:#ffecec 50%;">

                        <span style="font-weight:bold; text-transform:uppercase;">it can't be done.</span></div>'

                );

A brute way of doing it is:

die("it can't be done.");

Or you can:

SugarApplication::appendErrorMessage('<div style="color:#555; border-radius:10px; font-family:Tahoma,Geneva,Arial,sans-serif;font-size:11px; padding:10px 10px 10px 36px; margin:10px; border:1px solid #f5aca6; background:#ffecec 50%;">

                        <span style="font-weight:bold; text-transform:uppercase;">it can't be done.</span></div>'

                );

It worked, thank you so much.