TIBCO WebService : "WS Security Error : 8"

Hi, What does the following error code mean : "WS Security Error : 8" ? We have a TIBCO webservice controlled by a user / password type "WS-Security" (UserNameToken inbound). When we call this webservice from SOAPUI, we get this error: "WS Security Error: 8". This error is reported ONLY on computers whose operating system is Windows 10. On a Windows 7 computer, the same call from a SOAP UI works perfectly ... Thank you for your help.