AD7770 memmap crc error

Hello!

I use AD7770 with variable sps, and set new sps value approximately every 2ms. 

Measurements are correct, but the ADC produces an error MEMMAP_CRC_ERR.

Any other error flags is zero (Including any SPI errors).

According to the documentation, I have to reset the ADC when this error occurs, but it occurs about 10 times per second, which is clearly incorrect work.

If I do not change SPS, then there are no errors. SPS are in a valid range, from 8 to 16kSps.

What is the cause of such an error?