Most php servers have a default maximum file size of 2mb in place, this is not a limitation of form builder, but a limitation of the php sderver itself.
if you are not sure what the maximum is on your server, you can create a a new php file and add the following code to it:
<?php phpinfo(); ?>
this will display all of the php.ini settings including the max upload file size.
the php directives from the link i sent you would need to be set in the php.ini file on your server, if you are unsure on how to change these, you would need to contact the host.
the Problem Loading Page error could mean that a php error occurred, but error reporting is turned off.
you can try adding the following code to line 1 of the page to see if it returns a more descriptive error: