Issue replaying VUgen script against Oracle Forms 12c application

I am on client site and when I replay my (very basic login logout) vugen script it is failing with the following error:

Unsupported Java Class: oracle.forms.webutil.clientinfo.GetClientInfo

I have upgraded to LR 12.56 so the creation of the Webutil array is now automated which makes life much easier.

I have installed the JDK1.8 on my client desktop and updated Java to V8 R162 which I believe should be enough to get things to run.

I did have a script running against another build of this app, but this was configured as a Development environment whereas this one is configured as a Live environment - not sure if this is what is killing me from a permissions perspective?

The app servers are running on Linux now - when we last successfully tested this (7 years ago, Oracle 10g), they were running on Windows so quite a change in the architecture of the application under test.

Anyone got any eperiences of something similar?

This is killing me dead.