There are a couple of documentation errors on the API reference page at http://developer.authorize.net/api/reference/index.html
In the documentation for Void (the one about 2/3 down on the page, for use on transactions that have not been captured yet, the one in a div with id "homeresp-void", not the one in the "homeresp-void-a-transaction" div), the description of the transaction response has the "messages" subelement of the transactionResponse element at the wrong nesting level. It should have one bullet in front of it, but it has none. (And its child elements have one too few bullets).
In the documentation for Get Customer Profile IDs, the request has an extra merchantAuthentication element at the end.
Another one: in the Credit A Bank Account documentation, under the transactionRequest element, the payment, solution, and profile subelements are in the wrong order.
In Authorization Only and Authorization and Capture, under the transactionRequest element, the solution and lineItems are in the wrong order. shipTo is also in the wrong place.
In Credit, transHash and testRequest are in the wrong order.
There may be many more. I noticed the above by noticing places where a given element appears in more than one transaction type in the documenation, but with common subelements in different order, and then checked the scheme to see which one was right. This means I only caught instances of the wrong order when there was another instance with those subelements in the documentation in the right order.
The ARBCreateSubscriptionRequest API reference indicates the `billTo` can have a `phoneNumber` and `faxNumber`. This appears to be incorrect based on API error responses I'm receiving as well as the XSD.