@Berdir mentioned this issue to me today on IRC.
Relevant code from twig.engine:
<?php
if (is_object($arg)) {
if (method_exists($arg, '__toString')) {
return (string) $arg;
}
throw new Exception(t('Object of type "@class" cannot be printed.', array('@class'=> get_class($arg))));
}
?>If possible we should mention the variable name as well as the template where this is being called from - that would be a big improvement.