Ah, now I see what happened, you downloaded the old, obsolete and 'security'-hampered AutoIt release, that tries to get the data from the Excel file by opening it using Excel and then using select-all/copy to clipboard. There are issues with that method, as reported by others in that thread, giving the exact same error...
All these issues are resolved by the completely rewritten 2.x (Java) release, that can be downloaded from my dcmembers page, referenced in that thread (typing this on the tablet, so quite difficult to add the link here, sorry).
Maybe you could try that version.
I removed the AutoIt-based files from the Excel2Html thread.