Create artwork error

Hi, experts

I found there was a post named "Create Artwork Error" posted last year, while there is some differences in my case.

My OS is windows7 32bits, Allegro PCB Design XL (Legacy), 16.6 S008(v16-6-112AD) [4/16/2013]

When I was trying to create gerber, this error happened.

//////////////////////////////////////////////////////Part of log///////////////////////////////////////////////////////////////////
  APERTURES USED:
  ---------------------------------------------------------
  TYPE       SIZE/NAME                   ROT   MIRROR MODE
  ---------------------------------------------------------
  CIRCLE     0.01600                                  DARK
  CIRCLE     0.01800                                  DARK
  CIRCLE     0.02000                                  DARK
  CIRCLE     0.02200                                  DARK
  CIRCLE     0.02400                                  DARK
  CIRCLE     0.04000                                  DARK
  CIRCLE     0.04800                                  DARK
  CIRCLE     0.05200                                  DARK
  CIRCLE     0.05400                                  DARK
  CIRCLE     0.05600                                  DARK
  CIRCLE     0.06000                                  DARK
  CIRCLE     0.06300                                  DARK
  CIRCLE     0.06400                                  DARK
  CIRCLE     0.08700                                  DARK
  CIRCLE     0.11700                                  DARK
  CIRCLE     0.12100                                  DARK
  CIRCLE     0.15500                                  DARK
  SQUARE     0.04000                     0.000 NO     DARK
  SQUARE     0.04800                     0.000 NO     DARK
  SQUARE     0.05400                     0.000 NO     DARK
  SQUARE     0.05600                     0.000 NO     DARK
  SQUARE     0.06000                     0.000 NO     DARK
  SQUARE     0.06300                     0.000 NO     DARK
  SQUARE     0.06400                     0.000 NO     DARK
  SQUARE     0.12600                     0.000 NO     DARK
  RECTANGLE  0.01100     x 0.02900       0.000 NO     DARK
  RECTANGLE  0.01100     x 0.02900      90.000 NO     DARK
  RECTANGLE  0.01100     x 0.07000       0.000 NO     DARK
  RECTANGLE  0.01100     x 0.07000      90.000 NO     DARK
  RECTANGLE  0.01500     x 0.02700       0.000 NO     DARK
  RECTANGLE  0.01600     x 0.07000       0.000 NO     DARK
  RECTANGLE  0.01600     x 0.07000      90.000 NO     DARK
  RECTANGLE  0.02500     x 0.08000       0.000 NO     DARK
  RECTANGLE  0.02500     x 0.08000      90.000 NO     DARK
  RECTANGLE  0.03000     x 0.04800       0.000 NO     DARK
  RECTANGLE  0.03300     x 0.02200       0.000 NO     DARK
  RECTANGLE  0.03300     x 0.02200      90.000 NO     DARK
  RECTANGLE  0.04000     x 0.03500       0.000 NO     DARK
  RECTANGLE  0.04000     x 0.03500      90.000 NO     DARK
  RECTANGLE  0.04000     x 0.11000      90.000 NO     DARK
  RECTANGLE  0.04400     x 0.09600      90.000 NO     DARK
  RECTANGLE  0.04600     x 0.05100      90.000 NO     DARK
  RECTANGLE  0.04800     x 0.16700       0.000 NO     DARK
  RECTANGLE  0.04800     x 0.16700      90.000 NO     DARK
  RECTANGLE  0.05200     x 0.01600       0.000 NO     DARK
  RECTANGLE  0.05200     x 0.01600      90.000 NO     DARK
  RECTANGLE  0.07000     x 0.01100      90.000 NO     DARK
  RECTANGLE  0.07000     x 0.01600       0.000 NO     DARK
  RECTANGLE  0.07000     x 0.01600      90.000 NO     DARK
  RECTANGLE  0.07000     x 0.06900      90.000 NO     DARK
  RECTANGLE  0.07300     x 0.10800       0.000 NO     DARK
  RECTANGLE  0.07300     x 0.10800      90.000 NO     DARK
  RECTANGLE  0.07500     x 0.02500       0.000 NO     DARK
  RECTANGLE  0.07500     x 0.07100       0.000 NO     DARK
  RECTANGLE  0.07500     x 0.07100      90.000 NO     DARK
  RECTANGLE  0.07500     x 0.08100       0.000 NO     DARK
  RECTANGLE  0.07500     x 0.08100      90.000 NO     DARK
  RECTANGLE  0.07900     x 0.09400      90.000 NO     DARK
  RECTANGLE  0.10000     x 0.06500       0.000 NO     DARK
  RECTANGLE  0.10000     x 0.06500      90.000 NO     DARK
  RECTANGLE  0.10200     x 0.10400       0.000 NO     DARK
  RECTANGLE  0.10200     x 0.10400      90.000 NO     DARK
  RECTANGLE  0.10200     x 0.13600       0.000 NO     DARK
  RECTANGLE  0.10200     x 0.13600      90.000 NO     DARK
  RECTANGLE  0.13400     x 0.11000       0.000 NO     DARK
  RECTANGLE  0.13400     x 0.11000      90.000 NO     DARK
  RECTANGLE  0.42500     x 0.32800       0.000 NO     DARK
  RECTANGLE  0.42500     x 0.32800      90.000 NO     DARK
  OBLONG     0.04400     x 0.12700       0.000 NO     DARK
  OBLONG     0.10700     x 0.06000       0.000 NO     DARK
  FLASH SYM  20_DIAMOND                  0.000 NO     DARK
  FLASH SYM  20_DIAMOND                 90.000 NO     DARK  (undefined)
  FLASH SYM  20_DIAMOND                180.000 NO     DARK
  PAD SHAPE  20X20CHAMPER              270.000 NO     DARK


    ERROR: aborting film - Undefined aperture symbol, cannot continue.
           See APERTURES USED table in this file for symbols to provide.
////////////////////////////////////////////////////////////////////////////////////////////////////////

It seems I used a Flash Symbol, 20_DIAMOND, but Allegro can't find in library. I wanted to know which pad was using this flash symbol, and I can draw one myself. So I wen to Tools->Padstack->Modify Design Padstack.., I went through all these pads one by one, but I didn't find it. Is there any other way to find it, or I should set some parameters before generating gerber?

Any input would help.

Thanks.

Chris