External Cron disabled?

Hi,

Just setting up aMemeber and setting up the Cron Job now.

directly accessing /cron.php gives me the following error:

An Error has occured
External cron disabled in setup


Where abouts do I have to go to enable this? I can;t for the life of me find the option.

OK, I am now getting the below error in email:

/web/cgi-bin/php5: Symbol `client_errors' has different size in shared object, consider re-linking
Set-Cookie: PHPSESSID=tml16aqf3vm6dnqs3glo9phcv5; path=/
Expires: Thu, 19 Nov 1981 08:52:00 GMT
Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0
Pragma: no-cache
Content-type: text/html; charset=ISO-8859-1

However no errors in "aMember Admin error/debug log".

My hosting is with GODADDY, and I am running the following command:
/web/cgi-bin/php5 "$HOME/html/members/cron.php"

Any help would be great alex, cheers