So I got into a chat session with an Authorize.net support person .. end result they were contacting engineering ... they suggested I fix my cart to cope with their changes, but I am not "zenned" enough to figure that one out. Hopefully the log below will help someone post a fix.

Welcome to the Authorize.net chat forum. For your security, account updates can’t be processed through chat. Please don’t send any credit card or SSN information. For further help, please visit our Knowledge Base: http://www.authorize.net/help
You are currently at position number 1 in the queue. An Authorize.net representative will assist you shortly. We appreciate your patience.
You have been connected to Brandon S.
Brandon S: Hello Sharni! How can I help you today?
Sharni : Morning Brandon
Sharni : I use zencart and authorize.net is no longer working with my cart as of yesterday
Sharni : it processes transactions, takes the money, but no order comes through my system
Sharni : So I went to zencart forums to see if the fault laid there.
Sharni : http://www.zen-cart.com/forum/showth...777#post903777
Sharni : Seems I was not alone
Sharni : Apparently any zencart user that uses authorize.net is having the same problem
Brandon S: What is the error being returned?
Sharni : are you able to access that post I just linked to you?
Sharni : Towards the bottom someone has figured out the problem on your end
Sharni : it has to do with your API and the decimal places being increased to 4 from 2
Sharni : There has been an error processing your credit card. Please try again.
Sharni : This is the error I get on my cart end
Brandon S: Please hold while I review your account information. Thank you.
Sharni : There is no email error being sent to me from you. As you guys are processing payment.
Sharni : ok
Brandon S: It seems like it has to do with the md5 hash. Let me see if the are others reporting this issue.
Sharni : ok
Brandon S: Ok we do not have any further information at this time. I am going to have to escalate this issue and I can email you back once I have some more information.
Sharni : Thank you. Should I turn it off on my cart in the meantime?
Sharni : Just direct people through paypal for now
Sharni : I dont want frustrated customers
Brandon S: Or you can remove the md5 hash from your cart. That is what seems to be causing this issue.
Sharni : Ok I will see if I can figure out how on earth I can do that
Brandon S: You just need to remove the variable from your script.
Sharni : This is software that I am not that familiar with the back end of
Sharni : I do some modifications, but not to that depth
Sharni : I installed the authorize.net module as you guys were recommended
Sharni : and to date its been working fine
Sharni : There is an option under the set up that has my putting in an encryption key for MD5 Hash
Sharni : Do I just take out the key?
Brandon S: Yes that is correct.
Sharni : Ok trying that now and will run a test transaction right now
Brandon S: Ok
Sharni : That didnt work.
Sharni : Still got an error
Sharni : And the system just billed my credit card
Brandon S: We need more specifics. That is just a general error zen cart is displaying. We need the specific reason code that is being returned when the transaction is passed to us.
Sharni : yeah that is just being passed to the customer.
Sharni : Let me see if there is log files I can turn on
Brandon S: Ok
Sharni : ok in the auth.net module there is such an option, but there is no error at that end, so nothing is being generated.
Sharni : I am not saavy enough to figure it out in zencart
Brandon S: Unfortunately that is not something we can assist with. We do not work directly with zen cart.
Sharni : understand
Sharni : however it is a change made by your end that is causing zencart to error
Brandon S: Unfortunately at this time we do not have any specifics or more information to give you. I will pass this information on our engineers then email you once I have some more information.
Sharni : ok I guess that is the best we can do. I will turn off CC payments for now and leave it with just paypal
Sharni : Thank you for your time.
Brandon S: Thank you for contacting Authorize.Net Support, Sharni! Please contact us if you need further assistance. If you would like a copy of this session for reference, click on the "Print" icon.
Thank you for using Authorize.Net. Please search our new online Knowledge Base for answers to Frequently Asked Questions: http://www.authorize.net/help
Your session has ended. You may now close this window.