FT2232 device not accepting address x, error -71
the XTAL is 12MHz instead of 6MHz


Changing the crystal frequency from the manufacturer-specified 6 MHz value is not allowed and will prevent correct behaviour, since that 6 MHz clock input is used to generate a 48 MHz clock (see the FT2232D block diagram on datasheet page 4) used by the USB Serial Interface Engine and DPLL for timing.

For example here on page 8, the XTIN pin is described as a 6 MHz input:



Datasheet section 7.0 - Oscillator Configurations - also lists only a 6 MHz crystal or ceramic resonator frequency.

I recommend that you use an appropriate 6 MHz crystal and re-test.