Hi,

not sure if your Oscillator is set to the correct frequency. 20MHz; should this not be 48MHz? Are you defining the configs correctly for use with PLL?

For a 20MHz crystal I use these:

Code:
    'Config1L
'    Full-speed USB Clock Source Selection: Clock Source from 96MHz PLL/2
'    CPU System Clock Postscaler: Prescaler Divide by 5 for 20MHz Crystal
'    96MHz Prescaler: Divide by 5 (20MHz Input) 
@ __CONFIG _CONFIG1L, _USBDIV_2_1L & _CPUDIV_OSC1_PLL2_1L & _PLLDIV_5_1L

    'Config1H
    'Oscillator: HS oscillator, PLL enabled, HS used by USB
    'Fail-Safe Clock Monitor Enable: Enabled
    'Internal External Switch Over Mode: Disabled
@ __CONFIG _CONFIG1H, _FOSC_HSPLL_HS_1H & _FCMEM_ON_1H & _IESO_OFF_1H
Cheers

Rob