You referral link can only remove the code from payment list at check payment step.If you set error message at session (Mage::getSingleton('core/session')-&gt;addError(Mage::helper('payment')-&gt;__('Code is not avaliable.')))  on function isAvaliable  it can be shown on next step.

According my concept it will be good idea to do something at methods.phtml where all payment method has been listing during the checkout.

&lt;?php
$isCodeAvalibale=0;
    foreach ($this-&gt;getMethods() as $_method):
        $_code = $_method-&gt;getCode();
    if($_code =='cashondelivery'):
    $isCodeAvalibale=1;
    endif;
    endforeach;
if($isCodeAvalibale==0):
echo Mage::helper('payment')-&gt;__('Code is not avaliable.'));
endif;
?&gt;


display error message under payment method if "COD " is not available
I have site column with the following formula:

[AmountLeftToPay]/([AmountAssigned]-[AmountReleased])

The problem is the division by zero, sometimes it shows on list items #DIV/0!

So I wanted to do the following:
=IF([AmountAssigned]-[AmountReleased]=0; 0; [AmountLeftToPay]/([AmountAssigned]-[AmountReleased]))

And it shows me the same error in all lists where its used.
is not supported.
/apps/xx/xx/Lists/Budgets : The formula contains a syntax error or is not 
supported.

If I change ; with commas,
The formula contains a syntax error or is not supported.

so I got no clue
