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?
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 [firstname.lastname@example.org] Senior Consultant, Microsoft Consulting Services, UK