Hotfix KB2550886 may need to be install on a Windows 2008 R2 Server before applying Exchange 2010 Service Pack 3.
Thanks Yuval Sinay And Taken from the Blog Yuval Sinay Link Blog
As you can see in the following screenshot, hotfix KB2550886 is reported as prerequisite for Exchange 2010 Mailbox Role upgrade.
Please note: Installation of Hotfix KB2550886 may required a complete server reboot.
The Hotfix KB2550886 can be download from the following link.
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