dont know if you fixed the input to an output as barry suggested but i think that the problem

you can remove the pullup option as they are turn off anyway if outputs
the calibration setting in osccal seems to be cleared during an erase on this chip
so setting the register if you need to it adjust may be needed , but other wise id not worry if it just blink a led
i would also recommend a more up to date IC such as 12F683 as the new designed chips have very similar instruction / register setups which make it easy to go to other new chips when learning a PIC

hope it helps

Cheers

Sheldon

Code:
#CONFIG
  __config _INTRC_OSC_NOCLKOUT & _WDT_OFF & _PWRTE_ON & _MCLRE_OFF & _CP_OFF 
 
#ENDCONFIG

OSCCAL = %100000                ' 4MhZ - Set calibration register to Center Freq - Note Erasing the device also clears the calibration value for internal osc

CMCON        = 0               ' Comparators not used 
TRISIO        = %00000000       ' set all GPIO as outputs  - Note Master clear pin GPIO is not used 
OPTION_REG.7 = 0                 ' Set Week Pullups globle off    . Note when GPIO  SET AS output Week pullups  is automaticly turned off 


DEFINE OSC 4            ' Timing reference for pause , pauseus commands 

Start:

toggle GPIO.0
pause 1000         ' pause of 1sec 

goto Start

End