actually I did read them - that's where I got your error code. But seemed to me that there is always the possibility that the new site with the issue may be configured differently than your other site. I am assuming it is also an AbanteCart - but you didn't specify
I have many clients using Authorize net without issue, so am assuming something within your settings or site is not correct yet.
Good Luck
I will not waste my time or yours further in try to assist