This has been steadily escalating this afternoon and the decision has finally been taken to remove RU4 from the download servers.  From what little I know one of the changes that was made to fix a bug in Exchange has highlighted a latent problem within Outlook.  Both the Exchange team and the Office team are looking into this issue.

What should you do?

  • If you haven't yet installed RU4, do not begin a rollout and do not deploy RU4
  • If you have already installed RU4, contact Microsoft Customer Support obtain an interim update which fixes the issue.

RU5 is due for release in August and contains a change within Exchange that prevents this apparent data loss from occurring.

The full update is here..
http://blogs.technet.com/b/exchange/archive/2011/07/13/exchange-2010-sp1-ru4-removed-from-download-center.aspx

Neil Johnson [neiljohn@microsoft.com]
Senior Consultant, Microsoft Consulting Services, UK