I would guess that port 80 is being used by something, preventing the client from launching the local web server. Try doing a netstat - a | more at a command prompt and see if port 80 is in use. Skype is a frequent offender.  Its was announced at LS that in 8.5.3 you'll be able to set the port in the Notes client to something other than port 80 to avoid these conflicts. (BETA Disclaimer: 8.5.3 is beta code, and the features discussed may not be in the final shipped product, etc, etc) ... In the meantime try to isolate what uses port 80 and shut it down while doing your preview.