This question may be related to a resolved thread.
Although I have checked the thread, I can confirm that all my add-ons are up to date, including Matrix, yet I am still getting the following error any time I try to create or edit a custom channel field:
An Error Was Encountered
Unable to load the requested file: admin/field_edit.php
I did an upgrade from 2.1.3 to the latest 2.2.2 (Build: 20110801)
Please help me out - I really need to get this site ready for the client ASAP.