Invoice email does not send out when completing payment using Paypal

Oct 06 15:57:11  [info] $backTrace = #0 ../sites/all/modules/civicrm/CRM/Core/Error.php(364): CRM_Core_Error::backtrace("backTrace", TRUE)
#1 ../sites/all/modules/civicrm/CRM/Core/DAO.php(1018): CRM_Core_Error::fatal()
#2 ../sites/all/modules/civicrm/CRM/Contribute/Form/Task/Invoice.php(479): CRM_Core_DAO::getFieldValue("CRM_Contact_DAO_Contact", NULL, "display_name")
#3 ../sites/all/modules/civicrm/CRM/Contribute/BAO/ContributionPage.php(922): CRM_Contribute_Form_Task_Invoice::printPDF((Array:1), (Array:2), (Array:1), NULL)
#4 ../sites/all/modules/civicrm/CRM/Core/BAO/MessageTemplate.php(508): CRM_Contribute_BAO_ContributionPage::addInvoicePdfToEmail("550", "303")
#5 ../sites/all/modules/civicrm/CRM/Contribute/BAO/ContributionPage.php(412): CRM_Core_BAO_MessageTemplate::sendTemplate((Array:13))
#6 ../sites/all/modules/civicrm/CRM/Contribute/BAO/Contribution.php(2291): CRM_Contribute_BAO_ContributionPage::sendMail("303", (Array:34), TRUE, FALSE)
#7 ../sites/all/modules/civicrm/CRM/Core/Payment/BaseIPN.php(853): CRM_Contribute_BAO_Contribution->composeMessageArray((Array:28), (Array:9), (Array:34), FALSE, FALSE)
#8 ../sites/all/modules/civicrm/CRM/Core/Payment/BaseIPN.php(788): CRM_Core_Payment_BaseIPN->sendMail((Array:28), (Array:9), (Array:7), (Array:34), FALSE, FALSE)
#9 ../sites/all/modules/civicrm/CRM/Core/Payment/PayPalIPN.php(290): CRM_Core_Payment_BaseIPN->completeTransaction((Array:28), (Array:9), (Array:7), Object(CRM_Core_Transaction), FALSE)
#10 ../sites/all/modules/civicrm/CRM/Core/Payment/PayPalIPN.php(343): CRM_Core_Payment_PayPalIPN->single((Array:28), (Array:9), (Array:7), FALSE, FALSE)
#11 ../sites/all/modules/civicrm/extern/ipn.php(52): CRM_Core_Payment_PayPalIPN->main()
#12 {main}