You have a superfluous pair of single quotes around the $POST['pswrd1'] value. Should be:
$register_data = array(
'username' => $_POST['username'],
'first_name' => $_POST['first_name'],
'last_name' => $_POST['last_name'],
'address' => $_POST['address'],
'postcode' => $_POST['postcode'],
'country' => $_POST['country'],
'e_mail' => $_POST['e_mail'],
'pswrd1' => SHA1($_POST['pswrd1']),
'phone_no' => $_POST['phone_no']
);
PS: notice how a little formatting makes things easier to debug, and using this forum's [noparse]
...
[/noparse] tags makes it easier for us to debug?