Axisfault running Workbench

We’ve had this issue on 2 systems now - one an upgraded 5.7 to 6.5.2, one on a clean 6.5.2 install.

On the Workbench connection dialogue after attempting to connect to a system the connection fails with the message:

“An unknown error message occurred but no error message was supplied. The received error was: org.apache.axis.AxisFault”

Help appreciated as always.