I am glad to inform you that we have addressed an issue concerning RadTreeView and Office2007Black in the Service Pack which we released the last Friday. Here is a line for this in our SP1 Release Notes:
"FIXED: There is an exception when setting the ThemeName property of RadTreeView to Office2007Black."
I believe that this will solve the issue that you currently experience as well. You can update to SP1 through our Visual Studio Extensions.
Let me know if you have additional questions.
the Telerik team