Write Protect Error re-flashing /dev/nor0.barebox

[Jerry Kirk]

We are updating from 2012-03 to 2012-09 and after flashing our SOM
(Phytec PCM043 - imx35) we starting getting this error:

barebox:/ erase /dev/nor0.barebox
                                     
erase: Operation not permitted

It worked the first time, when overwriting the 2012-03 image and booted, etc.
We have tried a few intermediate Barebox versions and think it worked up to 2012-
07.

Any ideas what we now need to do to be able to overwrite Barebox?