See the problem here? The so-called "grammar-checker" has not corrected a single grammar error in the text. The fact that there are no grammar errors to be corrected in the sample is hardly an excuse--how can I trust a "grammar checker" program that can't tell the difference between spelling and grammar? I doesn't.
In addition to the daily games at M-W.com, I highly recommend the daily game called Common Knowledge here: http://www.puzzability.com/cgi-bin/commonknowledge.pl