OK solved the issue as follows
the private_key.pepk path was set to desktop so I changed it to the same folder as the jks
I then got an error saying android studio/xojo could not find the jarsigner.exe when building the file . It seems that xojo is looking for jarsigner in android studio/jre/bin but its in android studio/jbr/bin
eventually I copied all contents of the jbr to jre and all works as it should.
Not sure if its my system settings are wrong or xojo looking in wrong place. I guess the may be a better way getting things in the right place this one worked for me.