If your M128 is manufactured prior dec-2003 it may contain the following bug.
By reading flash memory with 'lpm/elpm' att maximum clockrates
the read value may be invalid.
This for instance affects your system if you do a checksumming
of the code at start-up.
We have only experienced this at max clock (16MHz).
Don't know if this also affects reading of data/strings in flash nor the
We have found this in about 3-5% of our M128's.
Atmel do since dec-03 additional test to sort bad chips out.
Yes, Atmel support has confirmed this.