Log in to Checkbox from another application

[sp11180]

I am trying to integrate Checkboxes into an existing application and running into an issue.
When we integrated with ultimate survey I was able to make a remote request to the login page passing username and password in order to authenticate prior to launching the survey. I am unable to do this for checkboxes with the new login.aspx page. I did however come across the following forum thread : http://www.prezzatech.com/community/...plication.html
This looks as though it is exactly what I want to do although it is not working so I assume I am doing something wrong.
Below is the link I am building to edit the survey response:
http://xxxxx/Survey.aspx?s=c8b39065-...hold_id=183720
This works fine (I get the survey pre-populated with the previous response) as long as I open the link in a browser window where I have already logged into checkbox.
So in order to force the log in I am attempting to pass the userGuid too as described in the previously mentioned forum post. My new link looks like this:
http://xxxxx/Survey.aspx?s=c8b39065-...0-ce2127e941f6
Unfortunately this link isn’t working. It doesn’t appear to be authenticating the user as I thought it would so I am getting an empty survey page (no pre populated response) even if I open the link in a browser window where I have already logged into checkbox.
Any assistance you can give me with this would be greatly appreciated
Thanks

[sp11180]

Nevermind, I figured it out...
I needed to change the security on my survey to all registered users. I had it as public so it was ignoring the userGuid that I was passing in the querystring.