Written
Whle this error messags shows up on ChronoForms pages it isn't a ChronoForms bug. Some Joomla! modules use the Joomla! JModel class without loading it - they assume that it will already be loaded.
This works OK if the module is on an article page but ChronoForms doesn't use JModel and has no need to load it so the module generates the error message.
The workaround is to add this code in a Custom Code action in the On Load event of your form:
<?php
jimport('joomla.application.component.model');
?>
This will load the missing class so that it is available for the module to use.
Thanks to the CB forums for this fix.