Thanks, that rules that out as a cause.
I'm confused because I've seen conflicting articles about the contents of the locked.properties file. One suggested I should add the top three lines below. Another article had a public and private key in there as well.
clientHost=servername.com
clientPort=443
clientProtocol=https
storetype=jks
keyfile=xxxx.jks
keypass=secret
Can anyone post the contents of a working locked.properties file? Much appreciated