VMware Support AlertVMware has become aware of an issue where an upgrade to vSphere 5.5 may fail when upgrading the SSO component. The issue appears to be related to the default SSO certificate generated when installing vSphere 5.1 Build #799735

For details and updates on this issue refer to KB article: vSphere 5.5 Single Sign-On upgrade rolls back after importing Lookup Service data (2060511)

Related info:

Location of Single Sign On log files for vCenter Server 5.1 (2033430)