You probably have error_display turned on in your php.ini file. That line would produce a deprecated message warning you that it won't work once you update to php 7. You may have to turn off deprecated messages (it won't effect the functionality of the page). That will prevent it from printing the error and allow the redirect to proceed.
If you give me FTP access and a URL with steps to reproduce the error I could try turning off deprecated messages on the page to confirm that is the cause.
Did this help? Tips are appreciated...
