The webshop shows a page error during the checkout process.
In the Authorize.NET section of the frontend web config, there is an IP check performed. This checks the IP address returned from Authorize.NET and ensures it fits into a certain range.
This problem applies to web shops that use Authorize.NET as their payment gateway, and use an API with an unknown IP address.
Find the Authorize.NET section in the frontend web conig and modify the IPCheck IPaddress range. Add the offending IP address to the range as long as it is verified by Authorize.NET as being legitimate.
Some known IP addressese which have cause this problem: 220.127.116.11, 18.104.22.168, 22.214.171.124, 126.96.36.199
These can be added to IP range: 64.94.*.*|127.0.0.1