Hello arvolund,
Yes, we already know that such problem appeared recently. Please open a /googlecheckout/classes/gCart.php file
and find the following function:
function output($xml_data, $GCheckout_button,$GCheckout_button_w, $GCheckout_button_h, $GCheckout_button_loc, $GCheckout_button_style)
{
and replace the
<?php echo $merchant_id;?>
with this:
<?php echo $this->_merchant_id;?>
This will fix the button.
P.S. Google recently have added a merchant id check in the button generation, so we need to post him the true one.
Best,
Alex