Exchange 2010 autodiscover not working internally

I am having issues with autodiscover not working internally.

Environment: 1 Exchange 2010  SP2 RU 2 server having CAS+MB+HTS role which was migrated from Exchange 2003

Issue details: Auto configuration of outlook profile works fine internally but OOF/FB/OAB is not working.
I have checked the autodiscover internal URL and other web services virtual directory internal URL which are set properly.

I am using a wildcard certificate with SN as  *.mydomain.com.au for myExchange server
and the internal/external url for for autodiscover internal URL and other virtual directories are set to owa.mydomain.com.au. When I am running test-outlookwebservices, I can see the valid SCP is returned but can not be contacted -error-(502) Bad Gateway.
)

[PS] C:\Windows\system32>Test-OutlookWebServices

RunspaceId : f5c4ba5c-9742-4423-9db5-579f4d6535d5
Id         : 1019
Type       : Information
Message    : A valid Autodiscover service connection point was found. The Autodiscover URL on this object ishttps://mail.mydomain.com/Autodiscover/Autodiscover.xml.

RunspaceId : f5c4ba5c-9742-4423-9db5-579f4d6535d5
Id         : 1013
Type       : Error
Message    : When contacting https://mail.mydomain.com/Autodiscover/Autodiscover.xml received the error The remote serv
             er returned an error: (502) Bad Gateway.

RunspaceId : f5c4ba5c-9742-4423-9db5-579f4d6535d5
Id         : 1023
Type       : Error
Message    : The Autodiscover service couldn't be contacted.

RunspaceId : f5c4ba5c-9742-4423-9db5-579f4d6535d5
Id         : 1113
Type       : Error
Message    : When contacting https://exchsrv01.mydomain.com.au:443/Autodiscover/Autodiscover.xml received the error The
             underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel.

RunspaceId : f5c4ba5c-9742-4423-9db5-579f4d6535d5
Id         : 1113
Type       : Error
Message    : When contacting https://exchsrv01.mydomain.com.au:443/Autodiscover/Autodiscover.xml received the error The
             remote certificate is invalid according to the validation procedure.

RunspaceId : f5c4ba5c-9742-4423-9db5-579f4d6535d5
Id         : 1123
Type       : Error
Message    : The Autodiscover service couldn't be contacted.

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[PS] C:\Windows\system32>Test-WebServicesConnectivity | fl

RunspaceId                  : f5c4ba5c-9742-4423-9db5-579f4d6535d5
LocalSite                   : WPSite
SecureAccess                : True
VirtualDirectoryName        :
Url                         :
UrlType                     : Unknown
Port                        : 0
ConnectionType              : Plaintext
ClientAccessServerShortName : exchsrv01
LocalSiteShortName          : WPSite
ClientAccessServer          : exchsrv01.mydomain.com.au
Scenario                    : GetFolder
ScenarioDescription         : Issue an Exchange Web Services GetFolder call to retrieve a folder.
PerformanceCounterName      : CreateItem Latency
Result                      : Failure
Error                       : [System.Net.WebException]: The underlying connection was closed: Could not establish trus
                              t relationship for the SSL/TLS secure channel. Inner error [System.Security.Authenticatio
                              n.AuthenticationException]: The remote certificate is invalid according to the validation
                               procedure.
UserName                    : extest_d94c2ba3ac0e4
StartTime                   : 12/25/2013 4:12:45 PM
Latency                     : -00:00:01
EventType                   : Error
LatencyInMillisecondsString :
Identity                    :
IsValid                     : True

The certificate is a public trusted certificate which is valid.

 I did some research but nothing helped me. Any help/ suggestion will be appreciated.

Regards,

Imrul