"Could not establish trust relationship for the SSL/TLS secure channel"

During the configuration of DUET_E , when calling the DUET Application from SharePoint, the following error is shown :

"Could not establish trust relationship for the SSL/TLS secure channel with authority 'MYSAPNW702SERVER:8001'"

I have already seen the Post :

error-in-duet-configuration-at-ssl

This mentions the error, but does not provide any answers on resolution.

The DUET_E troublshooting guide suggests that the SAP Standard SSL Certificate is added to SharePoint Central Admin > Security > Manage Trusts

This has also been done.

We are using the Standard SAP SSL Self signed certificate - not one signed by an external CA.

Can anyone provide any guidance ?

Thanks in advance.