Membership Plugin (Edit Profile Error)

I have just integrated Membership into my wordpress site and everything is running smoothly except for when someone tried to update their account info. When they hit submit, this pops out:

Catchable fatal error: Object of class __PHP_Incomplete_Class could not be converted to string in home/content/76/6749876/html/wordpress/wp-includes/functions.php on line 1526

On line 1526, this is the code that is present:

$array[$k] = addslashes( $v );

I'm not exactly sure what the problem is here, and any help would be greatly appreciated.