... and you had a previous version installed? Try this (courtesy David Wortendyke): Uninstall the current SDK by running BizTalk Services SDK Setup.exe . Go to <WindowsDir>\Microsoft.NET\Framework\v2.0.50727\CONFIG and open machine.config . Go to the bottom and remove the <system.servicemodel> section and all its contents. You'll know it's the right section if you see the extensions for relayBinding and other " relay " related elements. Note that you should be careful editing this file. Consider making a backup first and verify you are deleting the right section. Use gacutil.exe /u <assembly> to remove ChannelFx.dll and Microsoft.ServiceModel.Relay.dll . Reinstall the current BizTalk Services SDK Setup.exe . HTH.
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