I found a working program from steve in another thread:
@ DEVICE MCLR_ON, INTRC_OSC, WDT_ON, LVP_OFF, BOD_OFF, PWRT_ON, PROTECT_OFF, CCPMX_ON
OSCCON=$60 ' use internal 4MHZ osc
PAUSE 100 ' start-up delay
TRISB=0
DEFINE CCP1_REG PORTB
DEFINE CCP1_BIT 3
HPWM 1,128,1000
HERE: GOTO HERE

I just change the oscillation to 20Mhz, and it si not working: I think this is the problem..
I change the program to:

@ DEVICE MCLR_ON, HS_OSC, WDT_ON, LVP_OFF, BOD_OFF, PWRT_ON, PROTECT_OFF, CCPMX_ON
DEFINE OSC 20 'use external 20mhz crystal 'OSCCON=$60 ' use internal 4MHZ osc
PAUSE 100 ' start-up delay
TRISB=0
DEFINE CCP1_REG PORTB
DEFINE CCP1_BIT 3
HPWM 1,128,1000
HERE: GOTO HERE