Non-static method PEAR::isError() should not be called statically
The form code was generated using an old version of Simfatic Forms. Your web server was upgraded to PHP 5 (or above). So PHP is throwing error that the code is old and need to be upgraded
Upgrade to the latest version of Simfatic Forms. Then open the form, regenerate the code and re-upload the form. This will update the form code to the latest.
It is possible to suppress the 'Deprecated' error in PHP configuration settings. You have to get help from your hosting service. Request your hosting service to disable 'deprecated' error messages. See this page for details.