Vault is unable to render an Excel document that contains a header or footer. There is no data in the body of the document.
Since there is no data in the body of the document, it is technically a blank document which makes Vault unable to render the document.
The first thing to test with most MS Office documents that do not render is to go to the source document. Use the Print to PDF function on the source document itself. This is very similar to the engine Vault uses to create Renditions.
When doing this on a document as described, the Office Document returns the error: We didn't find anything to print. This means the document does not render in Vault.
To avoid this problem, add data in the body of the document and Vault should be able to render the document.
Vault Rendition Documentation: Troubleshooting Renditions