Hi Shelby,
If you check the error into detail, is it saying that Object reference not set to an instance of an object? (you have to look inside the error message). When you have an error with Invoke code (other than assemblies and all that other stuff), you can check the real origin of the problem at the end of the log message:
This could be because you have to initialize the Powerpoint app–>
Dim ppt_app As Microsoft.Office.Interop.PowerPoint.Application = New Microsoft.Office.Interop.PowerPoint.Application
And you have to do the same with Excel application. I recomend that you test your code step by step.
Let me know if it works for you.