Update Rollup 5 for Exchange Server 2010 Service Pack 1 resolves issues that were found in Exchange Server 2010 Service Pack 1 since the software was released. This update rollup is highly recommended for all Exchange Server 2010 Service Pack 1 customers.
Get it here: http://www.microsoft.com/downloads/details.aspx?FamilyID=731d0ebd-f094-4a37-aafa-78e1052780c5
Description of RU 5 for Exchange Server 2010 SP1: http://support.microsoft.com/kb/2582113
Cheers,
Anderson Patricio
http://blogs.msexchange.org/patricio
Twitter: @apatricio