Cannot calculate the frequency error

[yourcomrade]

Hi, I am currently using your library for the ADF4351 chip with arduino uno. My ADF4351 board has a reference clock at 25 Mhz. I change the example code to generate 40 Mhz, Here is the main code file:

#include <Arduino.h>
#include "adf4351.h"

#define SWVERSION "1.0"

#define PIN_SS 9  ///< SPI slave select pin, default value

ADF4351  vfo(PIN_SS, SPI_MODE0, 1000000UL , MSBFIRST) ;
void setup()
{
  Serial.begin(9600) ;
  Serial.print("Hello adf4351 demo v") ;
  Serial.println(SWVERSION) ;
  Wire.begin() ;
  /*!
     setup the chip (for a 10 mhz ref freq)
     most of these are defaults
  */
  vfo.pwrlevel = 0 ; ///< sets to -4 dBm output
  vfo.RD2refdouble = 0 ; ///< ref doubler off
  vfo.RD1Rdiv2 = 0 ;   ///< ref divider off
  vfo.ClkDiv = 150 ;
  vfo.BandSelClock = 80 ;
  vfo.RCounter = 1 ;  ///< R counter to 1 (no division)
  vfo.ChanStep = steps[4] ;  ///< set to 100 kHz steps

  /*!
     sets the reference frequency to 10 Mhz
  */
  if ( vfo.setrf(25000000UL) ==  0 )
    Serial.println("ref freq set to 10 Mhz") ;
    else
      Serial.println("ref freq set error") ;
      /*!
         initialize the chip
      */
      vfo.init() ;

  /*!
     enable frequency output
  */
  vfo.enable() ;
}
void loop()
{
  /*!
     do a set of freq changes (40 Mhz, 4 GHz, and 1Ghz, )
  */
  vfo.disable();
  delay(2000);
  Serial.println("setf() to 40 MHz") ;

  if ( vfo.setf(40000000UL) == 0 ) {
    Serial.print("setf() success freq:") ;
    Serial.println(vfo.cfreq) ;
  } else {
    Serial.println("setf() error") ;
  }
  vfo.enable();

  Serial.print("PLL INT:");
  Serial.println(vfo.N_Int);
  Serial.print("PLL FRAC:");
  Serial.println(vfo.Frac);
  Serial.print("PLL MOD:");
  Serial.println(vfo.Mod);
  Serial.print("PLL PFD:");
  Serial.println(vfo.PFDFreq);
  Serial.print("PLL output divider:");
  Serial.println(vfo.outdiv);
  Serial.print("PLL prescaler:");
  Serial.println(vfo.Prescaler);
  Serial.println("");
  delay(2000);
}

I get this error:

setf() to 40 MHz
output freq diff than requested
Mod out of range
setf() error
cfreq: 22349
PLL INT:0
PLL FRAC:-23
PLL MOD:2147483246
PLL PFD:25000000.00
PLL output divider:64
PLL prescaler:0

It is weird because I also try to use Analog software to calculate, and it calculates that INT is 102, FRAC is 2, PFD is 25 Mhz, Div is 64.

I look at the code but still don't understand why it cannot calculate the right value like the software.