Please read documentation:
https://winscp.net/eng/docs/scripting#hostkey
https://winscp.net/eng/docs/scripting#hostkey
You have quotes all wrong. I do not know VBS, but I guess right format is:
sftpcmd = "winscp /console /command ""open sftp://nstcn61:password@10.10.1.100 -hostkey=""""ssh-rsa 1024 XX:XX:XX:XX:XX:XX:XX:XX:XX:XX:XX:XX:XX:XX:XX:XX"""""" ""put c:\sysaudit\*.*"" ""close"" ""exit"""
Read also:
https://winscp.net/eng/docs/commandline#syntax
Of course the XX:XX:XX... has to be replaces with actual fingerprint.