This usually indicates that there is something wrong with curl 's libraries.
The Datatex compiled curl that supported SFTP is no longer required on newer Ubuntu servers, since the version that comes with the server now supports it.
Running this command should show the correct result:
curl -V | grep sftp
Protocols: dict file ftp ftps gopher gophers http https imap imaps ldap ldaps mqtt pop3 pop3s rtmp rtsp scp sftp smb smbs smtp smtps telnet tftp
The amtexporter2 requires this to be able to export properly. If this script is using the Datatex compiled version, fix the script (amtexport.sh) to use the system version and comment out the LD_LIBRARY line.