This indicates an attack attempt against a Buffer Overflow vulnerability in ABB IDAL FTP Server.
The vulnerability is due to accepting an overly long FTP command from a remote, authenticated attacker. Successful exploitation overflows the buffer and terminates the FTP server process.
ABB PB610 Panel Builder 600 versions 1.91 to 220.127.116.117
Denial of Service: Remote attackers can crash vulnerable systems.
Apply the most recent upgrade or patch from the vendor.