Thanks for taking the time to offer assistance.  I would ask you - have YOU tried to attach an excel sheet to a forum post?  What I get when I attempt to do so is a deliberate message from the site giving me a list of allowed file formats (.jpg .pdf etc) and .xls is not on the list and the file does not post.  Do you get a different result when trying to choose an .xls file as an attachment?  Can you please post a test .xls file to verify it can be done?

I have attached the .xls file to this post, with the chosen file as you describe, and I clicked the "post" button with the following error from intuit (see attachment).