Permalinks – custom structure subpages not working

H Folks,

I can get http://www.site.co.uk/sample-post/ to work fine.

But when I try and access http://www.site.co.uk/sample-post/sub-post

I get a ‘oops cant find your page error’.

I have a .htaccess file and can write to it in wordpress.

Can anyone please help?

Thankyou