Most likely this means that your FTP server is not supporting CRC hashes (XCRC command).
You can use Ftp.GetSupportedHashTypes method to get hashes supported
by your server:
List<FtpHashType> hashTypes = ftp.GetSupportedHashTypes();
If you want hashing to work, you need to choose an FTP server that supports one of the following commands:
- XCRC,
- XMD5,
- XSHA,
- XSHA1,
- XSHA256,
- XSHA512
Please note, that using SSL/TLS eliminates the need of verifying hashes
FTP over SSL/TLS (FTPS) ensures your data stays intact during transfer.