Hi Sergio,

Above 25MHz, you'll need a TTL type clock oscillator. HS and HSPLL support
up to 25MHz primary osc.

Make sure you have the latest verion of the 4550 data sheet rev DS39632C
and look in the electrical characteristics section at table 28-8, parameter 1A.

With a 40MHz TTL type clock oscillator, and EC or ECIO oscillator modes, it
should work fine.

With this config you should still have full-speed USB, 40MHz CPU clock, and
have port function on RA6.

CONFIG PLLDIV=10,CPUDIV=OSC1_PLL2,USBDIV=2,FOSC=ECIO_EC