Port Error, Someone tell me something

[serial_bug]

Hi my friends,
I wrote my very simple program with pic basic pro version 2.6 and something went wrong. please check it my code

TRISB=0
Main:
PORTB = 7
PAUSE 200
PORTB = 0
PAUSE 200
GOTO Main
END

I put 3 LEDs in RB0, RB1 and RB2, I want all 3 LEDs want to be on and off. Here is the problem, all LEDs are on, but no OFF.
Someone can help me something? I used PIC16F628A with internal clock