I've moved to a new server with a current version of PHP, have updated WordPress to 4.5.2 and updated CiviCRM to 4.7.7. I still get this error when exporting selected records from an Advanced Search:
Warning: strpos(): Empty needle in /home/zoweh/public_html/allied/wp-content/plugins/civicrm/civicrm/CRM/Export/BAO/Export.php on line 709
Warning: Cannot modify header information - headers already sent by (output started at /home/zoweh/public_html/allied/wp-content/plugins/civicrm/civicrm/CRM/Export/BAO/Export.php:709) in /home/zoweh/public_html/allied/wp-content/plugins/civicrm/civicrm/CRM/Utils/System/Base.php on line 895
Warning: Cannot modify header information - headers already sent by (output started at /home/zoweh/public_html/allied/wp-content/plugins/civicrm/civicrm/CRM/Export/BAO/Export.php:709) in /home/zoweh/public_html/allied/wp-content/plugins/civicrm/civicrm/CRM/Utils/System/Base.php on line 895
Warning: Cannot modify header information - headers already sent by (output started at /home/zoweh/public_html/allied/wp-content/plugins/civicrm/civicrm/CRM/Export/BAO/Export.php:709) in /home/zoweh/public_html/allied/wp-content/plugins/civicrm/civicrm/CRM/Utils/System/Base.php on line 895
Warning: Cannot modify header information - headers already sent by (output started at /home/zoweh/public_html/allied/wp-content/plugins/civicrm/civicrm/CRM/Export/BAO/Export.php:709) in /home/zoweh/public_html/allied/wp-content/plugins/civicrm/civicrm/CRM/Utils/System/Base.php on line 895 "Contact ID","Contact Type","Contact Subtype","Do Not Email","Do Not Phone","Do Not Mail","Do Not Sms","Do Not Trade","No Bulk Emails (User Opt Out)","Legal Identifier","External Identifier","Sort Name","Display Name","Nickname","Legal Name","Image Url","Preferred Communication Method","Preferred Language","Preferred Mail Format","Contact Hash","Contact Source","First Name","Middle Name","Last Name","Individual Prefix","Individual Suffix","Formal Title","Communication Style","Job Title","Gender","Birth Date","Deceased","Deceased Date","Household Name","Organization Name","Sic Code","Unique ID (OpenID)","Current Employer ID","Contact is in Trash","Created Date","Modified Date","Addressee","Email Greeting","Postal Greeting","Current Employer","Location Type","Street Address","Street Number","Street Number Suffix","Street Name","Street Unit","Supplemental Address 1","Supplemental Address 2","City","Postal Code Suffix","Postal Code","Latitude","Longitude","Address Name","Master Address Belongs To","County","State","Country","Phone","Phone Extension","Email","On Hold","Use for Bulk Mail","Signature Text","Signature Html","IM Provider","IM Screen Name","OpenID","World Region","Website","Group(s)","Tag(s)","Note(s)","Phone Type","IM Service Provider"
It then lists each of the records selected in the same format...