Error empty PK with 3rd party plugin

I am creating a 3rd party plugin to create amember with our app.
Each time I try creating or deleting a user I get a database error even if the operation
is successful.
here is the create table code:

PHP:

public function createTable()
    {
        $GUID = getGUID();
        $table = new Am_Protect_Table($this, $this->getDb(), '?_users', 'GUID');
        $table->setFieldsMapping(array(
            array(":".$GUID, 'GUID'),
            array(Am_Protect_Table::FIELD_LOGIN, 'username'),
            array(Am_Protect_Table::FIELD_EMAIL, 'email'),
            array(Am_Protect_Table::FIELD_PASS, 'password'),
           
        ));
               
        return $table;
    }


where GUID is the PK in our app. (it has no autoincrement since we are using GUIDs)

The error I keep getting is
"Trying to update not a loaded Am_Record - PK is empty"

any help is appreciated