Remote Assistance invitation fails in an Active Directory environment in Windows 7 or in Windows Server 2008 R2

Symptoms

Consider the following scenario:

• There is a forest trust established between two root domains (root domain A and root domain B) in an Active Directory environment.

• There is a child domain in root domain A. For example, root domain A is child.domainA.com.

• There is a client computer in root domain B that is running Windows 7 or Windows Server 2008 R2.

• You are in the child domain in root domain A, and you log on to the computer in domain B.

• You open a Remote Assistance invitation to connect to another user's computer. The other user is also in domain A and is logged on to a computer that is amember of domain B.

In this scenario, the Remote Assistance invitation fails. Additionally, you receive an error message that resembles the following:

Cause

This issue occurs because Privilege Attribute Certificate (PAC) validation fails across Active Directory forests.

Resolution

Status

Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

More Information

To identify this issue, you can use a network trace by enabling Net logon debug logging on the authenticating domain controller in domain B. For more information about how to do this, click the following article number to view the article in the Microsoft Knowledge Base:

109626 Enabling debug logging for the Net Logon serviceNotes

• The computer that offers remote assistance is typically called the "Expert."

• The computer that receives the remote assistance is typically called the "Novice."

1. A network trace that is taken from the client computer that offers remote assistance during the problem resembles the following:

   Remote procedure call (RPC) bind request with Kerberos service ticket from Expert to Novice:

   MSRPC MSRPC:c/o Alter Cont: unknown UUID{00000001-0000-0000-C000-000000000046} Call=0x2 Kerberos: AP Request Ticket[Realm: child.domainA.COM, Sname: <novice user>] 

   Novice to Expert response:

   MSRPC MSRPC:c/o Fault: Call=0x2 Context=0x0 Status=0x721 Cancels=0x0 {MSRPC:125, TCP:122, IPv4:117}

   The status of 0x721 = RPC_S_SEC_PACKAGE_ERROR
   
   "A security package specific error occurred" in other words a Kerberos error occurred.
   
   To view a complete list of RPC return codes, visit the following Microsoft TechNet website:

   http://technet.microsoft.com/en-us/library/aa378645(v=VS.85).aspx

2. A netlogon.log from the authenticating domain controller (that is, the domain controller that the Novice uses for authentication) in domain B will show the following Privilege Attribute Certificate (PAC) verification request failure:

   [LOGON] RESOURCE: SamLogon: Generic logon of child.DomainA.COM\(null) from (null) (via RESOURCE-WIN73) Package:Kerberos Entered 
   [LOGON] RESOURCE: SamLogon: Generic logon of EMEACHILD.LINDOM.COM\(null) from (null) (via RESOURCE-WIN73) Package:Kerberos Returns 0xC0000064

   0xc0000064 = STATUS_NO_SUCH_USER
   
   Important If you encounter this problem, you may have to do configuration changes to make Remote Assistance work across forests. For more information, click the following article number to view the article in the Microsoft Knowledge Base:

   2682075 Configuring Remote Assistance to work across forests

For more information about software update terminology, click the following article number to view the article in the Microsoft Knowledge Base:

824684 Description of the standard terminology that is used to describe Microsoft software updates