"RW access to 64KEXTFLASH and 8KEXTRAM"
Only the first 8k of flash is accessible for write.

If I understand correctly, you got thrown into some absent designers project. A couple of questions:

Are you modifying something that works ?
What instruments do you have available (ICE, scope, logic analyzer)?

Have you really checked the logic you describe, it does not make sense that the RW part of the flash is the first block

You talk abt 16k flash and 64k flash, what is it.

Have fun,

Erik