I’d stop wasting time trying to make it work. Simply save your spreadsheet (you are saving it early, often, and keeping duicates, right?), and just copy/paste the file into an email.

At one point I supported Office for Microsoft, and while they’d never admit it, this process for embedding files has alway been a little wonky (directly from one app to another). Grabbing the file and pasting it eliminates the risk of either app causing a problem because the OLE registration isn’t perfect, by using a file system path to the object.

I believe you can paste into Outlook a sheet as a table this way, if that’s what you’re trying to do. Not something I’d do, because, again, this kind of stuff has always been a little less than perfect. Attached files seem to have fewer issues.