I found the issue. In earlier pre-Excel versions of my script I had no problems opening files without a path, assuming the files were in the same folder as the script or compiled executable, which they were. Everything worked fine.
But with _Excel.au3, I got the error until I replaced $sourceFile with the full path. So that was the issue. Interesting enough, if I use a relative path ".\Test.xlsx" it opens a blank Excel instance and just sits there. Doesn't abort; doesn't open the spreadsheet.
So there you go, _Excel.au3 is limited in that it has to have a full file path, unlike the built-in FileOpen() which works fine without a full path.
Thanks for at least replying to my call for help.
