Geocoding Provider Error
Like William says, the error is due to the geocoding, which may even be happening after the contribution completes. Your system is trying to geocode with the domain http://query.yahooapis.com/ which no longer has a dns entry.

Chances are you are running a very old version of CiviCRM and need to upgrade it, but in any case, you can just remove geocoding in Administer -> System Settings -> Mapping and Geocoding, i.e. this path:

/civicrm/admin/setting/mapping?reset=1

You could install the new geocoding extension at some point, but I'd think your priority would be to get rid of the errors.