Error Domain=CBATTErrorDomain Code=128

I'm trying to write commands to the BLE module which operates a hardware. After I write the value to the characteristic in the following way :

NSMutableData *concatenate = [NSMutableData data];

uint8_t first=0xAB;

uint8_t second = 0x01;

uint8_t third = 0x01;

uint8_t fourth=0x0A;

uint8_t fifth=0xBA;

NSData* one = [NSData dataWithBytes:(void*)&first length:sizeof(first)];

NSData* two = [NSData dataWithBytes:(void*)&second length:sizeof(second)];

NSData* three = [NSData dataWithBytes:(void*)&third length:sizeof(third)];

NSData* four = [NSData dataWithBytes:(void*)&fourth length:sizeof(fourth)];

NSData* five = [NSData dataWithBytes:(void*)&fourth length:sizeof(fifth)];

[concatenate appendData:one];

[concatenate appendData:two];

[concatenate appendData:three];

[concatenate appendData:four];

[concatenate appendData:five];

[aPeripheral writeValue:concatenate forCharacteristic:aChar type:CBCharacteristicWriteWithResponse];

I'm getting the callback : "peripheral didWriteValueForCharacteristic:". In this callback I'm receiving the following error :

Error Domain=CBATTErrorDomain Code=128 "Unknown ATT error." UserInfo={NSLocalizedDescription=Unknown ATT error.}

I'm not able to find the error codes for CBATTErrorDomain anywhere. Any help to analyze the error would be really helpful?