Thank you for you advice. This was checked and not selected.
I raised a call with IBM and they asked me to check that.
After a few more suggestions they think it may be this.........
The error you are seeing in the browser might have to do with old JVM/Java applets. Please update Java on the affected server and see if this helps. The below tech note provides more info:
Title: Download re-signed Java applets for IBM Domino (January 2014)
Doc #: 1662233
URL: http://www.ibm.com/support/docview.wss?uid=swg21662233
But taking the server offline to do this is out of hours and wont be applied quickly.