I would first totally delete your TIF folder:
http://www.mvps.org/winhelp2002/delcache.htm
If no joy, courtesy of easynews.com (where folks routinely download files up
to 2GB):
Downloading large files over HTTP on the Internet can be tricky. To avoid
the frustration of broken or corrupt downloads, observe the following
suggestions when downloading ......:
1.. Never download any zip file or zip segment that is greater than 255
Megabytes (MB) in size. If your zip file is greater than 255 MB, use a
download manager to split the download into multiple parts.
This is a limitation of broken, or misconfigured, web cache servers
operated by your ISP. These cache servers behave in unexpected ways when
transferring files greater than 255 MB in size. They can induce corruption,
or premature session termination.
The cache servers are usually transparent. You can't tell they are in
place until they corrupt a download.
2.. Use a download manager when ever possible. Avoid downloading large
zips with your web browser. Configure your download manager to split your
download into numerous parts. Make sure that each download segment is less
than 255 MB. For example, if your zip file is 800 MB in size, you need to
split the download into 4 parts. The download manager will automatically
combine the parts into one whole file.
Not only does using a download manager increase reliability of downloading
large files over the Internet, they also increase your download speed.
We recommend ReGet
http://www.reget.com/ as a download manager. ReGet
supports SSL as well.
3.. Try to use the port 81 download links if possible. Most ISP's don't
send port 81 traffic through their cache servers. Using port 81, you can
effectively bypass your ISP's transparent cache servers. However, some ISP's
try to cache port 81 as well as the default web port 80.
Do not try to resume a download on a different port then the download was
started on. Your computer thinks that identical files on different ports are
different files. If you switch ports, instead of resuming the file, your
computer will start the download from the beginning.
4.. If you must use a web browser to download from the Zip Manager, make
sure the browser's cache is set to at least twice the size of the largest
zip file you plan to download. If you are using IE, make sure to check both
checkboxes under Tools|Internet Options|Advanced|HTTP 1.1 settings. You will
have to restart your browser for these changes to take effect.
5.. Under no circumstances should you use Netscape to download from the
Zip Manager. The Netscape browser has a broken implementation of the
HTTP/1.1 protocol. This causes Netscape not to resume unfinished/broken
downloads.
6.. Make sure you have the newest firmware in your cable/dsl router. This
is especially important for linksys routers. Older firmware versions
contained incorrect MTU values that caused corruption at high speeds.
7.. If you are unlucky enough to get a corrupt or broken zip file, use
PKZip to repair the zip and recover as many files as possible. PKZip has the
best repair algorithms compared to other utilities.
http://www.pkware.com/home_and_small_office/products/windows/pkzip/