resurento's solution also helped me upgrade my vCenter 5.0 installation to 5.5.
My SSO installation was failing. The error log said: "BootstrapAll returned actual error code 1603 (note this may not be 100% accurate if translation happened inside sandbox)Action ended 8:52:39: InstallFinalize. Return value 3."
I did the following:
1. Rebooted the server.
2. Deleted all the content in the folder %programdata%\VMware\CIS
3. Manually installed Vmware-python package from CD in folder: Single Sign-On\prerequisites\VMware-python.msi.
4. I started a Simple install again and the installation completed successfully.