cannot read/write to 16F690 data memory after CPD_ON

Hi everybody - this is my first post to this very valuable forum, made after having found no aswers to the topic.

Here it is the scenario: PBP 2.46, JDM programmer

@ device pic16f690, xt_osc, wdt_off, pwrt_on, mclr_off, protect_on, cpd_on, ieso_off, fcmen_off

I use data memory to store strings and setup dialogs for my app at programming time (DATA 0,1,0,...). Just after buring the pic, all the bytes in the data memory become FF (from the inside) and no READ/WRITE operations succeed, so after power off, besides my precious strings that never appear, all the information supposed to be saved are gone.

What I red is that 'DATA MEMORY IS INVISIBLE FROM THE OUTSIDE AFTER SETTING CPD', not from the CPU.

Am I doing something wrong?

Many thanks in advance for your help,
Andrea