[f2py] results are nearly the same

Hi everybody
I'm new to f2py, I have used successfully for a several fortran
functions but now i'm running on an issue.
I have fortran function that uses another auxiliar function and it
seems not so complicated

 FUNCTION VNORM(P,SI,XM)
      DOUBLE PRECISION TI,TJ,FO,PREC,PAS,T1,FTI,FTJ,DTI,DER,TI2
      FO=2.*P-1.D0
      PREC=.00000001D0
      S=1
      T1=1.D0
      TI2=.0000001D0
      TJ=0
      IF(FO)1,90,2
1     S=-1
      FO=S*FO
2     TJ=4.2D0
3     PAS=.5D0
      GO TO 11
10    T1=T1*PAS
11    TJ=TJ*T1
      FTJ=DER(TJ)
      IF(DABS(FTJ-FO)-PREC)90,90,13
13    IF(FTJ-FO)18,90,10
18    TI=TJ*PAS
      FTI=DER(TI)
20    TI2=TI*TI
      DTI=2./DEXP(TI2)/1.7724538509
      TI=TI+(FO-FTI)/DTI
      FTI=DER(TI)
      IF(DABS(FTI-FO)-PREC)90,90,21
21    TJ=TJ-(FTJ-FO)/(FTI-FTJ)*(TI-TJ)
      FTJ=DER(TJ)
22    IF(DABS(FTJ-FO)-PREC)91,91,20
90    TO=TJ
      GO TO 92
91    TO=TI
92    Z=SI/XM
      A=ALOG(1.+(Z**2))
      T=S*TO*1.414214
      FK=(EXP(SQRT(A)*T-A/2.)-1.)/Z
      VNORM=SI*FK + XM
      RETURN
      END

this is the function der():

      FUNCTION DER(X)
      DOUBLE PRECISION B1,B2,B3,B4,B5,A,DER,X,U,ZX,ZT,T,P,ARGUM
      B1= 0.319381530D0
      B2=-0.356563782D0
      B3=1.781477937D0
      B4=-1.821255978D0
      B5=1.330274429D0
      ARGUM=2*3.141592654
      A=1.D0/DSQRT(ARGUM)
      ARGUM=2.
      U=X*DSQRT(ARGUM)
      IF(U) 100,101,102
101   DER=0.D0
      RETURN
100   U=DABS(U)
      IER=1
      GO TO 103
102   IER=0
103   ZX=A*DEXP(-U*U/2.D0)
      T=1.D0/(1.D0+.2316419D0*U)
      ZT=B1*T+B2*T*T+B3*T*T*T+B4*T*T*T*T+B5*T*T*T*T*T
      P=1.D0-(ZX*ZT)
      IF(IER) 107,107,108
108   P=1.D0-P
107   DER=2.D0*P-1.D0
      RETURN
      END


F2PY compiles all ok, but results are not the same or in an aceptable
range from the originals.

I'm pretty newby with python and F2PY and i don't know how to debug
the generated code....this is the options i use:
python c:\python25\Scripts\f2py.py -c --fcompiler=gnu95
--compiler=mingw32 -lmsvcr71 -m pearson pearson.f90

How can i debug or identify the problem

thanks a lot