Typically this is caused by the full certificate chain not being passed correctly during a SOL/IDER session within SCCM. I'm assuming you are using a tiered certificate authority infrastructure (root CA -> policy CA -> subordinate (issuing CA).
Try place a copy of the Subordinate Certificate Authority certificate in the Local Computer - "Trusted Root Certificate Authorities" of the server or workstation that the Out Of Band Management Console is run from.
I have Root CA and Subordinate CA certificate in Trusted Root CA.
Have you got any other suggestions?
What version of SCCM are you seeing this problem with and what version of the WS-MAN translator are you using?