Thanks for your post and sorry for the late response.
To deal with your issue, please first manually refersh the TFS warehouse cube by invoking Warehouse control web service. Plesae take a look at this article for further information: http://msdn.microsoft.com/en-us/library/ff400237.aspx
And in addition, for your issue do not have trend line shown in the Burndown chart, please make sure that the Trend Start Date in the Brundown sheet in the arrange of the Dates field on the Settings sheet.
Please also take a look at these two threads which may be helpful for you;
Vicky Song [MSFT]
MSDN Community Support | Feedback to us
First of all, I want to thank you for your post.
I did everything according your instructions from this links, but I have other issue now.
As you can see in the picture below. I'm getting only "Trend Line" without "Remainig Work" and "Completed Work" lines.