Orders Won't Go Through ("Cannot Place Order")

[webdizzier]

I am working on a new Magento 2.0  store and am having trouble getting orders to go through consistently.  Occasionally, I have success, but most of the time I get a pop-up window that says, "Attention:  Cannot place order".  There's no error # or anything.  This is happening in Magento, not the gateway (Authorize.net).  It's not a problem with the API Login ID or Transaction Key.  I have searched the forums but haven't found a solution that matches my scenario.  The developer that installed Magento and a custom theme has also said it's a problem in Magento.  Has anyone else out there seen this and have a solution?

Thanks in advance for any help offered!  If you need more details or any specific info, let me know.

[richmondtandb]

I am facing the same issue with my Magento 2. Also, I am using Authorize.net Direct Post Method. I have also doubled checked my API login, Transaction Key and MD5 hash. Everything seems to be fine. Wondering what could be the problem. 

[MaierWerx]

I'm having the same issue with 2.1.0. In reading through the forums, it is a known bug. Hoping there is a 2.1.1 release with a patch soon.

[creatingdigital]

Anyone solve this yet?

[MaierWerx]

I was having this same problem, but no longer. There are two problems you might be having: 

1) there was a bug in 2.1 that was fixed in 2.1.1. After upgrading to 2.1.1, a number of issues have been resolved, and

2) Do you possibly have your Authorize.NET Direct Post set to "Test Mode"? If it is set to "Test Mode" you will get the "Cannot Place Order" error. Try taking it out of test mode and placing a small "Authorize Only" order. 

[garpik]

Possible cause of the error - previous request (save payment method).
I've have Magento ver. 2.0.8 and my problem is here:
vendor/magento/module-checkout-agreements/Model/Checkout/Plugin/Validation.php:80

$paymentMethod->getExtensionAttributes() is returned null and the script throws an exception