You might want to read that section of the wiki article a little bit closer, with special attention to the part that says:
"The above has been entered as two lines. If entered in one line, remove the backslash ()"
That is actually all one command , broken into two lines for the sake of the wiki and to make a more "manageable" command line. You are only entering the first part of the command, and that is the source of the problem. The error message is telling you to use the -awstatsprog option (of the awstats.pl program) to "solve the problem", and that "option" is the last "half" of the "long" command line (or the "second line" - joined to the first with the "\") indicated in the wiki.
In other words, both "lines" are to be combined into one command line, OR you can use the "\" to "join" the two lines into a single shell command.