I have tried installing the WPF 2250 Service Release but error still persists

Andrew, can you send me the source code location for Infragistics 9.1 version? We would like to try the fix you have suggested. Lot of our customers are reporting this issue so we are planning to provide the fix without upgradation. 

Thanks Alan and Andrew for your replies. Now we are also trying to upgrade to latest version. I'm in the process of validating 11.1 version with last said scenario. I see that 11.1 is the latest version available. Could you please confirm the fix is available in this version? And 11.1 version is latest version?  

Andrew/Alan, At this stage we are analysing both options, update the source code with the fix suggested by Alan and upgrading to latest version. We'll take a decision based on less expensive approach.

I was able to download the source code and reach method GetChildrenCore(). Can you please check if below change is correct and it will fix the issue?

Or please suggest me the exact piece of code. I've one more question of the steps involved in compiling the binary and deploying once the fix is finalized which I'll defer to my next post. 

/// <summary>
  /// Returns the collection of child elements of the object that is associated with this <see cref="AutomationPeer"/>
  /// </summary>
  /// <returns>The collection of child elements</returns>
  protected override List<AutomationPeer> GetChildrenCore()
  {
   AutomationPeer peer = this.GetUnderlyingPeer();

   if (null != peer)
   {
    try
    {
     System.Reflection.MethodInfo method = typeof(AutomationPeer).GetMethod("UpdateSubtree", System.Reflection.BindingFlags.Instance | System.Reflection.BindingFlags.NonPublic);

     if (null != method)
      method.Invoke(peer, Type.EmptyTypes);
    }
    catch (SecurityException)
    {
    }

                if (null != peer.GetChildren())
                    return peer.GetChildren();
                else
                    return new List<AutomationPeer>();
   }

   return null;
  }

Andrew, apart from strong name issue, I'm getting two more compilation issues after changing the reference to local assembly which has the fix. I did verify that the dll has the interface but not sure what is missing

Error 11 The type 'Infragistics.Windows.Selection.ISelectableItem' is defined in an assembly that is not referenced. You must add a reference to assembly 'Infragistics3.Wpf.v9.1, Version=9.1.20091.1006, Culture=neutral, PublicKeyToken=7dd5c3163f2cd0cb'. 

Error 12 The type 'Infragistics.Windows.Helpers.DependencyObjectNotifier' is defined in an assembly that is not referenced. You must add a reference to assembly 'Infragistics3.Wpf.v9.1, Version=9.1.20091.1006, Culture=neutral, PublicKeyToken=7dd5c3163f2cd0cb'. 

Please let me know solutions for these.

Thanks Andrew,I'll take the code. Now I'm unable to build our assembly and compilation failiing because Infragistics3.Wpf.v9.1 is not signed with strong name. Could you suggest any work around for this issue? 

Error 10 Unknown build error, 'A strongly-named assembly is required. (Exception from HRESULT: 0x80131044)'  

No. That is the actual issue - that the actual collection instance provided by the peer element is being returned. The change should be:

var list = peer.GetChildren();

if (list != null)
   return new List<AutomationPeer>(list);