Problems getting DigitalStrom Binding to work

Dear support community,

actually I am facing a problem getting the digitalStrom Binding to work.
I am running OH 1.8 on my raspberry PI 2.
OH is working fine and stable.

I followed the instruction mentioned in the DigitalStrom Binding description.
I think I was able to create and copy the certificate to DSS as well as importing it to the raspberry.
Unfortunately I could not get the bindig working.

Who can support?

openhab.log is showing following errors:
2016-02-10 20:33:39.627 [ERROR] [o.o.b.d.i.c.c.t.HttpTransport ] - IOException by executing jsonRequest: /json/system/loginApplication?loginToken=00d6d554158533766e2269c9d16f70147acaa4c8186713f9ede6d8dc303c2d93 ; sun.security.validator.ValidatorException: PKIX path validation failed: java.security.cert.CertPathValidatorException: Path does not chain with any of the trust anchors
2016-02-10 20:33:39.643 [ERROR] [o.o.b.d.i.c.c.t.HttpTransport ] - IOException by executing jsonRequest: /json/system/login?user=dssadmin&password=******** ; sun.security.validator.ValidatorException: PKIX path validation failed: java.security.cert.CertPathValidatorException: Path does not chain with any of the trust anchors
2016-02-10 20:33:39.644 [ERROR] [d.internal.DigitalSTROMBinding] - could NOT get session-token