RL-FlashFS not working with EKK-LM3S6965

Hi

I use example in C:\Keil\ARM\Boards\Luminary\ek-lm3s6965\RL\FlashFS\SD_File
and it only runs when clock is below 30MHz. If clock is set to 50MHz with
SysCtlClockSet(SYSCTL_SYSDIV_4 | SYSCTL_USE_PLL | SYSCTL_OSC_MAIN | SYSCTL_XTAL_8MHZ)

the function mmc_command() return a wrong code (0x81) instead of 0x01.