This is a quite common error on Outlook 2010 x64.

Error Code: An unknown error occurred, error code: 0×80070057
Symptom:  It occurs when you try to add a new Exchange account in Outlook 2010
                 And in most cases because you try to use the AutoAccountSetup to create the new account

Solution:

1. Manualy create the Outlook 2010 Profile using this tutorial.
a. Go to Control Panel / Select Small Icons from the right menu / Click on MAIL / E-mail Accounts / New / E-mail Account:

b. Select Manually configure server settings or additional server types, then click NEXT:

c. Select Microsoft Exchange or compatible service, then click NEXT:

d. Complete the next step with your exchange server and user name, then click on Check Name, andNEXT:

e. Click FINISH and enjoy your new account.

2. Install the hotfix for this error:

2281463 Description of the Outlook 2010 hotfix package (outlook-x-none.msp): August 31, 2010
http://support.microsoft.com/default.aspx?scid=kb;en-US;2281463

More information from Microsoft:

When you create an Outlook profile by using the Auto Account Setup process, a Lightweight Directory Access Protocol (LDAP) query is first performed to look up the user who is currently logged on. Then, this user’s e-mail address and Exchange server information is returned from Active Directory Domain Services. This LDAP query is successful in Outlook 2010, and the query is not the cause of the error message that is mentioned in the “Symptoms” section.

When you click Next in the Auto Account Setup process to connect with your server and finish creating the profile, Outlook 2010 has some new additional code (This code is not found in Outlook 2007) to make sure that you do not add the same Exchange account two times. This new code assumes that Autodiscover succeeds. And, it pessimistically assumes that if Autodiscover fails, you might be trying to add a duplicate Exchange account. Because Autodiscover is expected to fail in almost all configurations that involve an Exchange 2003 mailbox, this new code generates the 0×80070057 error.

In this scenario, you can force a successful Autodiscover connection by using a local Autodiscover.xml file and some registry data. This registry data forces Outlook to use a local Autodiscover.xml file for Autodiscover queries.

The following is an example Autodiscover.xml file:

<Autodiscover xmlns="http://schemas.microsoft.com/exchange/autodiscover/responseschema/2006">

  <Response xmlns="http://schemas.microsoft.com/exchange/autodiscover/outlook/responseschema/2006a">

    <Account>

      <AccountType>email</AccountType>

      <Action>settings</Action>

      <Protocol>

        <Type>EXCH</Type>

        <Server>E2K3.wingtiptoys.com</Server>

      </Protocol>

    </Account>

  </Response>

</Autodiscover>

Workaround

Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:

322756 How to back up and restore the registry in Windows

To use this workaround, follow these steps:

1. Create the Autodiscover.xml file by using the example in the More information section of this article as a template. Make sure that you enter your Exchange Server 2003 server name in the<Server> tag.
2. Save the file to either a local folder on the hard disk or to a network share that everyone can access.
3. On the Outlook client, deploy the following registry data:

Key: HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\Outlook\AutoDiscover

DWORD: PreferLocalXML
Value: 1

String: the name of your domain

Value: thepath of the Autodiscover.xml file that includes the file name

1. Create your Outlook profile by using the Auto Account Setup process.

ENJOY.

And if you encounter any problems feel free to comment / contact me.