The most common cause of this is an access restriction on the "/usr/bin/wget" utility used by the task. Sometimes, an alternative (http://listmailpro.com/forum/index.php?topic=957.0) must be used.
If you like to do things yourself, a small PHP script which may tell us the permissions of certain system utilities is below. Copy the code into a file named "test.php", upload it to your server and browse to it, then paste the results here. This is what I would do if I was doing a hands-on analysis of your server.
<?phpecho shell_exec('cat /etc/*rele*').'<br>';echo shell_exec('ls -al /usr/bin/wget*').'<br>';echo shell_exec('ls -al /usr/bin/curl').'<br>';echo shell_exec('ls -al /usr/bin/GET').'<br>';echo shell_exec('ls -al /usr/bin/lynx').'<br>';echo shell_exec('ls -al /usr/bin/fetch').'<br>';?>
If you want the easiest method, I recommend asking your web host what they suggest for a command-line to "browse to a URL each day".
Regards