try running the command from the prompt (not from cron) and see if you get an error that may help explain.
So, just log into ssh, and then paste in the "mysqldump --opt..." obviously you'll need to put in the user, pass, host name, and database name. but you leave the 'option' infront of it. Where is says -uUser, for example you would put in -umatttail. I know that part confused me at first. The same goes for the rest of the 'options'.
When I run the command I'm not returned with anything, just a new prompt, and the dump has been properly carried out. If you get an error, copy and paste it here.