After update, suddenly lost ability to access Windows Server 2008 R2 shares from Windows XP clients

Today I lost the ability to see my Windows Server 2008 R2 shares from any of my 3 Windows XP machines in my small office. The 5 Win7 machines haven't been affected (they are still able to browse/access the 2008 server), but none of my WinXP machines can access the 2008R2 server anymore. Yesterday (and for the previous year) everything was working fine. I do not have a domain setup. I can still access Win7 shares from WinXP clients.

Browsing the server logs, I see that the following update was installed last night:

> Installation Ready: The following updates are downloaded and ready for > installation. This computer is currently scheduled to install these > updates on ?Thursday, ?November ?15, ?2012 at 3:00 AM:  > - Security Update for Windows Server 2008 R2 x64 Edition (KB2761226) > - Security Update for Microsoft .NET Framework 3.5.1 on Windows 7 and Windows Server 2008 R2 SP1 for x64-based Systems (KB2729452) > - Windows Malicious Software Removal Tool x64 - November 2012 (KB890830) > - Cumulative Security Update for Internet Explorer 9 for Windows Server 2008 R2 x64 Edition (KB2761451) 

It seems likely that something was changed in last night's update, but so far I haven't seen anything on microsoft.com to prove it. I did hear that XP is reaching the end of the road soon. Any ideas?

Source: http://serverfault.com/questions/449270/after-update-suddenly-lost-ability-to-access-windows-server-2008-r2-shares-from

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