ORA-24806: LOB form mismatch
Cause: When reading from or writing into LOBs, the character set form of the user buffer should be same as that of the LOB.
Action: Make sure that the buffer you are using to read or write has the same form as that of the LOB.

ORA-24807: LOB form mismatch
Cause: When copying or appending LOBs, both source and desctination LOB locators should have the same character set form.
Action: Pass locators of the same character set form for copying or appending LOBs.