Operation Not Supported: LogonUser method in the Reporting Web Service

I'm getting a SoapException stating "This operation is not supported in
this edition of Reporting Services --> This operation is not supported
in this edition of Reporting Services" when I try to call
myReportService.LogonUser(myName, myPassword, myDomain)
I have verified that I am running the Enterprise edition of both Sql
Server + Reporting Services... is there anything else required in order
to use this function?
Here's the version info from my web service proxy:
ReportServerEdition "Enterprise"
ReportServerVersionNumber "Microsoft SQL Server Reporting Services
Version 8.00.743.00"
I get this error when I hit the service through both http and https. I
have an invalid cert on my development Report Server, which I'm
ignoring with System.Net.ServicePointManager.CertificatePolicy = New
CertificateIgnorer
where CertificateIgnorer is a custom class I wrote that always returns
true for any cert.
Is this error returned when ssl isn't working correctly?
Any help appreciated.Any ideas out there?