Thanks for clearing that up, erik.

Guy, it sounds like you're using a very similar setup. As I mentioned, the Intel D8752BH I have programs and erases fine, it's the AMD D8751H's that don't erase or program. The Intel datasheets state that the lock bit(s) will be erased by UV along with the rest of the array. I threw out my old AMD databooks long ago, and couldn't find an AMD data sheet online. A little more searching through the old Philips 8051 archives turned up the following:

http://www.semiconductors.philips.com/mcu/suppo.../0083.html

&

http://www.semiconductors.philips.com/mcu/suppo.../0104.html

It looks like it's not possible to erase the lock bits on 8751s from certain vendors, and my experience confirms it. Very interesting, indeed.