Earlier today the Exchange CXP team released an updated version of Update Rollup 4 for Exchange Server 2010 SP1
to the Download Center. This updated release is being made available
after a complete review and revalidation of the list of fixes included
in the previously released version of Rollup 4 dated June 22, 2011.

The review completed by the Exchange CXP team determined that the issue identified in 'KB 2581545:
The copy or move operation on a folder that contains subfolders does
not work as expected after you install Update Rollup 4 for Exchange
Server 2010 SP1 dated June 22, 2011’ introduced a serious regression in
the original release of Rollup 4. As a result, a new version of Rollup 4 dated July 23, 2011 has been tested and released with the change that caused the regression removed. The re-release of Rollup 4 is tracked by 'KB 2579150: Description of Update Rollup 4 for Exchange Server 2010 Service Pack 1'.

The updated Rollup 4 is being released to allow customers to install
the list of fixes previously committed to on the normal rollup schedule
using normal rollup installation routines without the need for further
action. The re-released version of Rollup 4 is functionally equivalent
to the combination of the original Rollup 4 release and (the interim updatein) KB 2581545. Here are answers to some install questions:

• Customers who have installed KB 2509910 (Rollup 4, dated June 22, 2011) and
  KB2581545 (fix for Rollup 4 regression) do not need to install KB
  2579150 (re-released Rollup 4) but may do so if they choose to.
• Customers who have already installed KB 2581545 and want to update
  their systems to the updated Rollup 4 should first uninstall KB 2581545
  (or any interim updates) prior to installing the new rollup.
• You do not need to uninstall original RU4 (KB 2509910) to install the re-released RU4 package (KB2579150).
• The re-release of Rollup 4 does not change the release plans for
  Update Rollup 5 for Exchange Server 2010 Service Pack 1. Rollup 5 is
  currently scheduled to release in August 2011.

Some of the above KnowledgeBase articles are not
replicated/live at the time of writing this post. Please check back
later in the day if you can't reach them.

General Notes

Note for Exchange 2010 Customers using the Arabic and Hebrew language version:
We introduced two new languages with the release of Service Pack 1,
Arabic and Hebrew. At present we are working through the process of
modifying our installers to incorporate these two languages. Customers
running either of the two language versions affected are advised to
download and install the English language version of the rollup which
contains all of the same fixes.

Note for Forefront users: For those of you
running Forefront Security for Exchange, be sure you perform these
important steps from the command line in the Forefront directory before
and after this rollup's installation process. Without these steps,
Exchange services for Information Store and Transport will not start
after you apply this update. Before installing the update, disable
ForeFront by using this command: fscutility /disable. After installing the update, re-enable ForeFront by running fscutility /enable.