Installation error 0x800b0101: System Center 2012 Configuration Manager Service Pack 1 Client.
This issue occurs because the MicrosoftPolicyPlatformSetup.msi file is signed with a digital certificate that does not have the proper timestamp attributes. Microsoft Security Advisory 2749665 has more information on this certificate issue.
Apply this hotfix before upgrading Clients,
Download HotFix here: http://support.microsoft.com/kb/2801987/en-us