CAN module clock configuration problem

I am using the STR912FA44 and I am implementing a CAN communication module.
I got an CAN example that uses the following uController clock configuration which works fine:

  SCU_MCLKSourceConfig(SCU_MCLK_OSC); // 25Mhz
  SCU_PCLKDivisorConfig(SCU_PCLK_Div2); // 8Mhz
  SCU_PLLFactorsConfig(128,25,4); // 16 Mhz
  SCU_PLLCmd(ENABLE);
  SCU_MCLKSourceConfig(SCU_MCLK_PLL);

It happens that I would like to use a different Pclk, once this clock is used for other modules, but if I change this values the module simply stops working ... my question is, Is there some kind of limitation concerning the Pclk in CAN module? Has to be 6 Mhz? I went though the ST documentation and I found nothing ...

Thanks for your help!