Imported users, problem with custom value

Hi, we started using s2member, now we imported the users from our old system (with another domain).
The problem now is that the ipn log shows the following

“0 => ‘IPN received on: Wed Jul 3, 2013 6:16:02 pm UTC’,
1 => ‘s2Member POST vars verified through a POST back to PayPal®.’,
2 => ‘Unable to verify `$_SERVER[“HTTP_HOST”]`. Please check the `custom` value in your Button Code. It MUST start with your domain name.'”

We searched the forum but on our old system we dont have a custom value in PayPal, we edited our old buttons from PayPal (in the paypal system) and added the custom value, but this will apply to our imported users?
We do have set up the subscription id to each customer but no custom value for identifying (as we dont have them registered with a custom value)
How can we fix this so the ipn works again for the old customers?

If PayPal doesn’t let you edit the subscription profile to add the custom value with your domain name, then I think you could try to solve this with an IPN script, which will fix the custom value before forwarding the notification to s2Member.

You can find a sample IPN script in the s2Member Pro Extras zip file, in your Account page. http://www.s2member.com/account/