Couldn't resolve host secure.authorize.net

[sltroup]

Credit card payments stopped working in cart.

Receiving the following errors:
Error: Couldn't resolve host 'secure.authorize.net'
Error: The transaction could not be completed.
Error: Failure in Processing the Payment (ps_authorize)

I am able to curl and browse secure.authorize.net from the web host.
I have confirmed that the ID and transaction key are correct.
Can anyone assist me with this?