1200163 - Error: "Your Security Context could not be verified. Please close your browser and try again" when logging on to BusinessObjects protected by Siteminder

When logging on to BusinessObjects XI Release 2 protected by Siteminder, the following error message appears:

"Your Security Context could not be verified. Please close your browser and try again. If the problem persists, contact your administrator"

CMS logs may look like the following:

trace message: secSSO: VerifyUser() Sm_AgentApi_DecodeSSOToken failed with return code: -1
trace message: ssoplugin: SSOImpl::ExternalSSOVerifyUser failed to verify user.
trace message: ssoplugin: SSOImpl::GetError() -- Could not get error details.
trace message: LDAP: AcceptLogin: Failed to verify SSO user
trace message: SecLdap Error: an unknown error occurred in AcceptLogin.
trace message: SecLdap Error: an unknown error occurred in AcceptLogin.
trace message: C3rdParty::AcceptLogin() -- 3d-party plugin returned an empty string as the alias.
trace message: C3rdParty::AcceptLogin() -- 3d-party login failed, but unable to determine for which user!