Error: No Preview available (Uploading PPTX)

Please explain the text at the  top of the image you enclosed
Who wrote it, on what website was my excel file embedded?
What does it tell you, about whom ,about what blog, and under what circumstances?
is your extension kosher?

I do not use a local server for testing this plug-in.
I am testng this on a lve website, but not available for the puplic yetuntil I am satisfied.
The pdf's and XLS files are uploaded to e folder in the root. pdf's work, XLS don't work

This is a very unprofessional answer: you ignore my questions regarding privacy, you just repeat how little you know.
I will vote using my legs by walking away. I now uninstall your unreliable plugin

good luck..