Can't edit transaction from /admin/user/userpoints

Patch for this reported bug: http://drupal.org/node/167683

Steps to reproduce:
1) set errors to write to log and screen (/admin/settings/error-reporting)
2) enable userpoints moderation (/admin/settings/userpoints)
3) add user points to a user's account (/admin/user/userpoints/add)
4) view the list of points in moderation (/admin/user/userpoints)
5) click the edit link on one of the transaction lines (/admin/user/userpoints/edit/2) (warning appears here)
6) try to edit point total (on submission, point total does not change)