session.user.uuid" was not found in the local cache for session

I am setting up APM for Exchange 2013. Authentication is working over LDAP, but Single Sign-On is not working. I am getting the following error in the APM log.

debug apd[28518]: 01490000:7: ./AccessPolicyProcessor/Session.h func: "getSessionVar()" line: 317 Msg: variable " session.user.uuid" was not found in the local cache for session

Does anyone know how to resolve the error?

Thanks.