If you are having problems installing any Role or Feature on a Server 2008 or Server 2008 R2 machine this may help, I was having an issue with the RPC over HHTP feature but this could potentially stop any role or feature from been installed correctly.
If the installation fails saying the server needs a reboot and the following error 'hr: -2147021879 -> reboot required.' is found in the log 'C:\windows\log\servermanager.log' try the following;
- Under HKEY_LOCAL_MACHINE\COMPONENTS delete 'PendingXmlIdentifier' (take a backup before deleting any reg keys)
- Delete the following file: c:\windows\winsxs\Pending.xml file and then reboot. You may need to take ownership of the file
- After the reboot try to install the role or feature again