Oracle Error Message
ORA-39269: Cannot alter a column of type LONG to anything other than LOB.
Reason for the Error
DBMS_METADATA_DIFF was comparing two table columns, the first of type LONG, the second of a data type other than LOB. There is no SQL ALTER statement to modify a long data type to anything other than a CLOB or NCLOB.
Solution
The difference cannot be eliminated with an SQL ALTER statement.