MailMan.VerifySmtpConnection problem

I'm using the CkMailMan object's VerifySmtpConnection method to verify SMTP details. In a previous build of the Chilkat library (from about a year ago) this worked fine. With the latest version (downloaded last week), however, it is returning false for exactly the same code. This is the lastErrorText after the failed response (a few details altered for privacy):

ChilkatLog:
  VerifySmtpConnection:
    DllDate: Dec 12 2012
    UnlockPrefix: [...snipped...]
    Username: NICK:Nick
    Architecture: Little Endian; 32-bit
    Language: Visual C++ 9.0
    VerboseLogging: 1
    Checking TCP/IP connectivity to the SMTP server.
    This does not check the login/password.
    AutoFix: SMTP port 25 is typically for unencrypted or explicit SSL/TLS.
    To prevent auto-fix, set the AutoFix property = False/0
    Checking connectivity to SMTP server [...snipped...]:25
    smtp_host: [...snipped...]
    smtp_port: 25
    ConnectTimeoutMs_1: 30000
    calling ConnectSocket2
    IPV6 enabled connect with NO heartbeat.
    connectingTo: [...snipped...]
    resolveHostname1:
      dnsCacheLookup: [...snipped...]
      dnsCacheHit: [...snipped...]
    --resolveHostname1
    GetHostByNameHB_ipv4: Elapsed time: 0 millisec
    myIP_1: 192.168.1.30
    myPort_1: 2520
    connect successful (1)
    clientHelloMajorMinorVersion: 3.1
    buildClientHello:
      majorVersion: 3
      minorVersion: 1
      numRandomBytes: 32
      sessionIdSize: 0
      numCipherSuites: 10
      numCompressionMethods: 1
    --buildClientHello
    readIncomingTls_serverHello:
      readTlsRecord:
        Timeout waiting to read socket or accept connection
        timeoutMs: 30000
        Failed to read TLS record (2)
        tlsRec_msg: 91
        msgLen: 8307
      --readTlsRecord
    --readIncomingTls_serverHello
    Expected ServerHello but did not receive it.
    Client handshake failed. (3)
    Failed to connect to SMTP server.
  --VerifySmtpConnection
  Failed.
--ChilkatLog

From the previous, working, build of Chilkat libraries, this is the last error text after VerifySmtpConnection succeeds:

ChilkatLog:
  VerifySmtpConnection:
    DllDate: Jan  6 2011
    UnlockPrefix: [...snipped...]
    Username: Nick
    Component: Visual C++ 9.0
    Checking TCP/IP connectivity to the SMTP server.
    This does not check the login/password.
    Checking connectivity to SMTP server [...snipped...]:25
    smtp_host: [...snipped...]
    smtp_port: 25
    ConnectTimeoutMs: 30000
    calling ConnectSocket2
    Connect using IPV4.
    Invalid protocol number
    ai_protocol: 0
    ipAddress: [...snipped...]
    socketHandle: 0x3d4
    ai_addrlen: 16
    ai_addr: 0200 0019 3EAC AF8A 0000 0000 0000 0000

    myIP_3: 192.168.1.30
    myPort_3: 2454
    connect successful.
    ESMTP server [...snipped...]:25 is reachable
    Success.

There's quite a lot different there. Where am I going wrong? I'm setting the SmtpHost, SmptUsername, SmtpPassword, SmtpSsl and SmtpLoginDomain settings before calling VerifySmtpConnection. I've tried with AutiFix set to true and false - same result.

To note, the Username field in the lastErrorText is different from the previous build to the current build; current build shows my machine name prefixed to my username (NOT the domain name), whereas previous build only shows the username (no domain or machine prefix).

Also if it is of interest, the test for the current chilkat build takes about twice as long as the previous one (though that may be due to it failing somewhere...).

Thanks for any advice!