Error "An unknown error occurred, error code 0x80070057" occurs when attempting to create additional mailboxes in Microsoft Office 2010 in conjunction with Microsoft Exchange 2003.
When Outlook attempts to configure additional mailboxes for an Outlook 2010 profile running under Exchange 2003, the settings are not correctly applied on the Outlook 2010 side. Sometimes an error will occur as well.
Microsoft has a hotfix available to fix this issue. The hotfix must be requested from Microsoft. Use the following link to submit your request.
Outlook 2010 hotfix package (outlook-x-none.msp)
