Hi Jeff,
This error typically indicates that TFSExtensionsTasksSetup.msi was not installed on the TFS Build Agent machine. Note that TFSExtensionsTasksSetup.msi should be installed on your Team Build 2008 Build Agent machine not on your local machine (unless your local machine has Team Build 2008 installed on it). I know it's a silly question, but can you confirm that you ran TFSExtensionsTasksSetup.msi on the TFS Build Agent machine and not on your local machine?