My checkout button has disappeared when I go to check out to go to Authorize.net. Why?

As of today, when an end user of E-Cart goes to check out, the first and second checkout buttons are there. However on the confirmation of order page, the button that used to be there to take them to Authorize.net does not show up anymore. I have contacted Authorize.net. None of the information that was there before has changed to cause this to happen. Please let me know what I can do to get the store working again. ! Here's the link to the store: http://lotcs.org/WA_eCart/cootie_depot.php. Thanks in advance

You are getting this error on the server:

Call to undefined function mhash()

This means that the mhash scripts are not enabled. They may have recently updated your server and didn't enable it. If you contact your hosting provider they should be able to enable MHASH and that will fix the issue.

Originally Said By: Ray Borduin

  You are getting this error on the server:

Call to undefined function mhash()

This means that the mhash scripts are not enabled. They may have recently updated your server and didn't enable it. If you contact your hosting provider they should be able to enable MHASH and that will fix the issue.  

Ray,
I just got off the phone with GoDaddy. The said that because I'm running PHP 5.4, the MHASH is no longer available. They suggested that I fix the code because it's outdated (according to them) and then my button will appear again. I've enabled "QuickHash" in version 5.4 and still no luck. Any help that you could provide so that I can get my button back, so that people can order stuff again would be greatly appreciated.
All the Best,
Dale

This post has been deleted.

Do you work for Web Assist? If so, please give me a number so that I can confirm your identity. Then we can set up a remote session if you like. I'm at work right now.
All the best...

Sorry I was logged in as another user to check their order history and forgot to log back in as myself before replying... I was the one that needs FTP access.

Can you do a remote session? My phone number is: 503-882-8621.

Ray,
I'm at work now with my computer.
Thanks,

Try updating the WA_simlib.php file...

find this line:
return (bin2hex (mhash(MHASH_MD5, $data, $key)));

and replace it with:
return (bin2hex (hash_hmac("md5", $data, $key)));

Ray,
Now the button shows up to check out, but I get this message: The following errors have occurred.
(99) This transaction cannot be accepted.
Authorize.net gave me a error code 99 tool at: http://developer.authorize.net/api/reference/responseCode99.html. But, the items that they want, I can't seem to find in the code on the Confirm.php page. I also activated the MD5 Hash tool on Authorize.net a couple of days ago. So, I don't know if I need to put the "Hash Code" that I created into the Confirm.php page. Please let me know what steps I need to take now. Thanks.
Dale