Set-IRMConfiguration -InternalLicensingEnabled $true failure

I'm trying to setup a test environment with AD RMS + Exchange 2010 and stuck in one step for several days.

[PS] C:\Windows\system32>Set-IRMConfiguration -InternalLicensingEnabled $true
The remote certificate is invalid according to the validation procedure. ---> The underlying connection was closed: Cou
ld not establish trust relationship for the SSL/TLS secure channel. ---> Failed to get Server Info from https://sha-dg-
rmssrv.dgvdi.com/_wmcs/certification/server.asmx.
    + CategoryInfo          : InvalidOperation: (:) [Set-IRMConfiguration], Exception
    + FullyQualifiedErrorId : C800E4A1,Microsoft.Exchange.Management.RightsManagement.SetIRMConfiguration

I followed guide below. Can anyone help? Looks like all Exchange IRM feature can't work if the InternalLicensing is not enabled.

http://technet.microsoft.com/en-us/library/ee849857(v=ws.10).aspx

http://www.msexchange.org/articles-tutorials/exchange-server-2010/compliance-policies-archiving/rights-management-server-exchange-2010-part1.html