I had this come up recently when trying to do an install. Earlier that day I had installed a new feature on the server (in this case the Windows Authentication feature of the Internet Information Services IIS role), but not done a reboot as one wasn't asked for.
However, the web client installation ended prematurely and it was only when I checked the Windows Event Viewer that I found the error relating to the pending reboot.
This was particularly annoying as the premature end was only after I clicked on the Install button after entering all of the required information at the preceding steps.
Based on this error, and when it appeared, from now on I am going to reboot the server I'm installing the web client before starting.