Using the payment processor PayPal_Standard on a fresh install of CiviCRM Version 4.7.29 (with Wordpress 4.9.1 on Centos 7.4) breaks all contribution pages where PayPal is enabled. The result is a blank page. In the Apache error log there is:
PHP Fatal error: require_once(): Failed opening required 'CRM/Core/.php' (include_path='.:/somedir/wp-content/plugins/civicrm/civicrm:/somedir/wp-content/plugins/civicrm/civicrm/packages:/somedir/wp-content/plugins/civicrm/civicrm/vendor/tecnickcom:/somedir/wp-content/plugins/civicrm/civicrm/vendor/phpseclib/phpseclib/phpseclib:/somedir/wp-content/plugins/civicrm/civicrm/vendor/pear/pear_exception:/somedir/wp-content/plugins/civicrm/civicrm/vendor/pear/auth_sasl:/somedir/wp-content/plugins/civicrm/civicrm/vendor/pear/net_socket:/somedir/wp-content/plugins/civicrm/civicrm/vendor/pear/net_smtp:/somedir/wp-content/plugins/civicrm/civicrm/ve in /somedir/wp-content/plugins/civicrm/civicrm/Civi/Payment/System.php on line 59, referer: https://someurl/civicrm/?page=CiviCRM&q=civicrm/contribute/transact&reset=1&id=1
When disabling PayPal (= pay later) the contribution pages work fine.
Any ideas what might be going wrong here?