don't just use http://domain-name.com/dev/build
or don't use http://domain-name.com/silverstripe/dev/build
My Silverstripe is installed on root (/) do I dont' have a sub-directory like 'silverstripe'.
What I used to get around the pain in the ass 404 errors I was getting in trying to run /dev/build was the following:
Now if you installed off of root, in a sub-directory, say it's called /silverstripe/ , then I would use...
By using the URL with /index.php/ I got the /dev to work, and /dev/build - both without needing to add the flush=1 or user= etc, etc.
Hope this helps out some of you with problems. ... As a newbie to S_S, I just stumbled on the solution by trial & error out of personal frustration.