This is urgent.
I have the same problem
Fatal error: Cannot redeclare class File_ft in /[removed]/system/expressionengine/fieldtypes/file/ft.file.php on line 365
when I try to access Administration -> Channel Fields through the CP, also if I go to Add-ons -> Fieldtypes.
Recently upgraded from 2.1.3 to 2.3.1 (build: date 20111017), and only noticed this after 2 days.
Tried solutions from thread above - they did not work. My install has ‘safecracker’ and ‘safecracker_file’ in third_party.
Also, my fieldtypes directory contains both folders, and individual files (of the same native fieldtypes, I think), if I delete the set of individual files - I get when trying to edit custom field sets
A PHP Error was encountered
Severity: Warning
Message: require_once(/[removed]/system/expressionengine/fieldtypes/ft.file.php) [function.require-once]: failed to open stream: No such file or directory
Filename: safecracker_file/ft.safecracker_file.php
Line Number: 3
Fatal error: require_once() [function.require]: Failed opening required '/[removed]system/expressionengine/fieldtypes/ft.file.php' (include_path='.:/usr/share/pear:/usr/share/php') in [removed]/system/expressionengine/third_party/safecracker_file/ft.safecracker_file.php on line 3