I'm getting the following error when trying to install DNN professional 6.1.5 using the web installer.  It fails on the last part of the install.  The pre-requisites install ok.  When i attempt to re-install, it recognises that the other components are already installs but still fails on the final step.  Any ideas?

System.ArgumentNullException was unhandled

  Message="Value cannot be null.\r\nParameter name: type"
  Source="System.Windows.Forms"
  ParamName="type"
  StackTrace:
       at System.Windows.Forms.Control.MarshaledInvoke(Control caller, Delegate method, Object[] args, Boolean synchronous)
       at System.Windows.Forms.Control.Invoke(Delegate method, Object[] args)
       at System.Windows.Forms.WindowsFormsSynchronizationContext.Send(SendOrPostCallback d, Object state)
       at Microsoft.Web.PlatformInstaller.InstallManager.SendProductInstallChainCompleted()
       at Microsoft.Web.PlatformInstaller.InstallManager.StartInstalling()
       at Microsoft.Web.PlatformInstaller.InstallManager.StartDownloadAndInstall(Object unused)
       at System.Threading._ThreadPoolWaitCallback.WaitCallback_Context(Object state)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
       at System.Threading._ThreadPoolWaitCallback.PerformWaitCallbackInternal(_ThreadPoolWaitCallback tpWaitCallBack)
       at System.Threading._ThreadPoolWaitCallback.PerformWaitCallback(Object state)

No, this is my first time using the web platform installer.  I'm only using it because I dont know were to source the DNN Pro Zip files.  It installed several components ok but the last step fails. 

I'm not 100% sure if I should be using the installer anyway but i just took a punt.  I'm installing on Win XP with SQL 2008 already installed prior to using the web installer.  

Cheers