Someone is having issues with SdFat library and IDE Arduino 1.8.1?
My connections seems corrects because I don't have any problem using a standard SD example (SD/ReadWrite). But I get this error when using SdFat library: errorCode:0x50, 0x20
Absolutely same behavior with me. Checked different speeds (4, 8 MHz) as greiman suggested here with no success.
/ using arduino pro mini 3.3v with MicroSD Card adapter)
OK after 10 hours of suffering, I solved the issue by changing the SD card module with another model (looking almost the same way) and now it's working.
This being said, try to replace the module, maybe there's something wrong with it.
Cheers