I had similar problems.
See here: https://firstname.lastname@example.org/msg13042.html
To keep a long story short:
As i can remember, i had 4 chips, 2 working and 2 not working.
Dont know why.
Option 1: Parts of the chip is write protected
Option 2: Chip is broken.
BTW: Strange "spispeed". Try with "30000"