The messages are in the Security log of the destination and are:
Event ID 537
Type: Failure Audit
User: NT AUTHORITY\SYSTEM
Computer: [destination server]
Description:
Logon Failure:
Reason: An error occurred during logon
User Name:
Domain:
Logon Type: 3
Logon Process: Kerberos
Authentication Package: Kerberos
Workstation Name: -
Status code: 0xC000006D
Substatus code: 0xC0000133
Caller User Name: -
Caller Domain: -
Caller Logon ID: -
Caller Process ID: -
Transited Services: -
Source Network Address: [IP address of FTP server]
Source Port: 0