Ant scp task has an attribute called trust. If set to false (default) the host you connect to has to be set in the knownhosts file (you might have to create it) Another way is to explicitly set "trust = true". Check the documentation: https://goo.gl/G5680x
Don't give up yet. Our experts can help. Paste your full stack trace to get a solution.
com.jcraft.jsch.JSchException: Auth fail
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
You have a different solution? A short tip here would help you and many other users who saw this issue last week.