Don't worry about the webrobot link not working; it's looking for an external (internet) address and you are operating locally, but this won't stop ACS.
you have obviously looked at the server logs - I find them very useful & suggest deleting the log then restarting nsd (to get a single load log) and scanning the log. You can see how ACS sets itself up, and spot any problems. Any event labelled "fatal" is usually that!
If you want to test it and can't run as root, setting the port to 8000 restarting nsd and logging in as localhost:8000 should work OK.
The locations of the error pages are defined in the "ad.ini" (your "compdb.ini"?) in the parameters directory under /web/{servername}.
