There was an unexpected error during the Delete Field tool process. This can happen when a file is in use by another program, the file is a read-only data source, or the input has read-only permissions.
If the input is a dBASE file (or a shapefile), the dBASE file must contain at least one field. Attempting to delete all fields will result in this error.
Check whether the table is locked by another user, is read-only, or can support deleting fields. You can try using different output files. If that doesn't work, try closing the application and running the tool again.