I presume the link is wrong, as it doesn’t include instructions. However, my best guess is that you forgot to make a file executable as that returns “permission denied” too. (In details, Linux has three permission read, write and execute for owner, group and all. Being root just makes you owner in a sense, but if the owner doesn’t have execute permission, then they will still receive permission denied.
My own guide expects basic level of Linux skills, which is the reason I’m hoping to get this done as an installable app at some point. I hate when installation needs to run shell commands from the Internet, specially if the user doesn’t understand them.