P89V51RB2FN can not erase

[nova]

  I have 2 kind of P89V51RB2FN, one 's label is white, and the other 's label is yellow. With white label kind, I have no problem. But with yellow label kind, I have a big problem: I can not erase Flash Rom. I can use Flash Magic to download program at the first time and it work properly (because at the first time, all Flash are 0xFF). After that, If I chose erase Flash from ISP menu, the Flash still keep the old value.
  I don't know how is different between two kind of chip have. The white label I had 6 month ago, and the yellow label I have just received them.

[Andy Ayre]

The color of labels doesn't tell me anything. However the numbers and letters printed on the casing of the device does. What do your devices have on them?

[nova]

 The full label is:
 P89V51RB2FN
 FA63-0662
 -zG0628 82

[Andy Ayre]

So the devices that work and the devices that don't have exactly the same letters and number printed on them? No differences?

[nova]

 The full label of the device work well is:
P89V51RB2FN
FA 460260
-Z 0442 B2

 And the device that don't work (can't erase normally) have the label:
P89V51RB2FN
FA63-0662
-zG0628 82

[Andy Ayre]

Thanks. I've forwarded this info to Philips.