If java is not installed i get this error in php debug mode when a user tries to register new account.

Notice [PHP]: Only variable references should be returned by reference in file include/functions.php line 491
Notice [PHP]: Only variable references should be returned by reference in file kernel/configitem.php line 97
Notice [PHP]: Only variable references should be returned by reference in file kernel/configitem.php line 100

Please help its leaving a blank page when not in debug mode.

Please check the read before you post link below and follow the instructions - if the FAQ on blank pages doesn't help please come back with your version information.