WebPortal SSO login issue

We are using OneIDM 8.1.1 and configured the HTTP Header (role-based) authentication as described in the below URL,

https://support.oneidentity.com/technical-documents/identity-manager/8.1.1/authorization-and-authentication-guide/21#TOPIC-1250085

As per the SSO logs (below) I see the HTTP headers are set properly,

[carms][/IdentityManager/page.axd][AD_DOMAIN\manide][User 'CN=manide,OU=Accts,DC=xyz,DC=qad,DC=abc,DC=com' is authorized by Policy Server.]
[carms][/IdentityManager/page.axd][AD_DOMAIN\manide][Calling SM_WAF_HTTP_PLUGIN->ProcessResponses.]
[carms][/IdentityManager/page.axd][AD_DOMAIN\manide][Processing Authorization responses.]
[carms][/IdentityManager/page.axd][AD_DOMAIN\manide][Removing HTTP cache request headers.]
[carms][/IdentityManager/page.axd][AD_DOMAIN\manide][Setting custom HTTP header variable: 'HTTP_EID=2776574822']
[carms][/IdentityManager/page.axd][AD_DOMAIN\manide][Setting custom HTTP header variable: 'HTTP_Username=277865748202']

But in the IDM trace log i see this error,

2020-08-25 03:33:10.2698 ERROR ( WebLog 4jckc0eyjyv3wueggxgsctyl) : VI.Base.ViException: Current user could not be determined.
at VI.DB.Auth.HttpHeaderHelper.GetSsoIdentity(IAuthProps props)
at VI.WebRuntime.Communication.SingleSignOnIdentityCheck.Execute(IRequestModuleInfo validatorModuleInfo)
at VI.WebRuntime.Communication.HttpModuleWebRuntime.ContextOnPreRequestHandlerExecuteInternal() VI.Base.ViException: Current user could not be determined.
at VI.DB.Auth.HttpHeaderHelper.GetSsoIdentity(IAuthProps props)
at VI.WebRuntime.Communication.SingleSignOnIdentityCheck.Execute(IRequestModuleInfo validatorModuleInfo)
at VI.WebRuntime.Communication.HttpModuleWebRuntime.ContextOnPreRequestHandlerExecuteInternal() at VI.DB.Auth.HttpHeaderHelper.GetSsoIdentity(IAuthProps props)
at VI.WebRuntime.Communication.SingleSignOnIdentityCheck.Execute(IRequestModuleInfo validatorModuleInfo)
at VI.WebRuntime.Communication.HttpModuleWebRuntime.ContextOnPreRequestHandlerExecuteInternal()