PHP: Fatal error: Can't use function return value in write context in .....

[yoda]

Fatal error: Can't use function return value in write context in /srv/www/htdocs/abcd/ui.php on line 2

I'm not firmiliar with this error message....

Line 2 in ui.php is...

<?php if (USER_TYPE_CHECK() = '0') {

USER_TYPE_CHECK() is a predefined function, have I used it wrong?