Bruce,

Don't know if others here can attest to something else but I've never being able to reliably download files of that size (or near that size) using URLDownloadToFile. The same applies several other mechanisms I have tested. For smaller files problems are rare but larger files (1 gb and above) reliability becomes an issue with a percentage of these becoming corrupt or fragmented/incomplete during the process.

Perhaps a comparison of filesize at the websource vs. the downloaded local file after a URLDownloadToFile is all that is needed. Other download mechanisms also use the IE download cache location and that is another venue of concern to avoid incomplete downloads.