I've successfully installed this extension(v1.7) in Civicrm 4.6 and created a payment processor omnipay_SecurePay_DirectPost.
But it always returns 'yoursite.com is currently unable to handle this request (HTTP ERROR 500)' after I filled in the credit card details and hit the submit button.
The website runs PHP5.6, Drupal 7 and Civicrm 4.6.
Any help would be appreciated.