Works fine here. Also, judging from the access logs of openrdf.org, there are lots of people that visit this site using IE 6.

I think you might find this intersting. It might be enough information to help reproduce the error. (Even though they refer to ASPs it should still correlate to some degress.)

Check out
 http://support.microsoft.com/default.aspx?scid=KB;EN-US;q316431&

SYMPTOMS When you attempt to open or download a Microsoft Office document (.doc file, .xls file, .ppt file, and so on) from a secure Web site in Internet Explorer, you may receive one of the following error messages, even though the document is available and downloaded from the server:

Internet Explorer cannot download file from server.

Internet Explorer was not able to open this Internet site. The requested site is either unavailable or cannot be found. Please try again later.
<DING><DING><DING><WE HAVE A WINNER!!!>

[snip]
CAUSE
In order for Internet Explorer to open documents in Office (or any out-of-process, ActiveX document server), Internet Explorer must save the file to the local cache directory and ask the associated application to load the file by using IPersistFile::Load. If the file is not stored to disk, this operation fails.

When Internet Explorer communicates with a secure Web site through SSL, Internet Explorer enforces any no-cache request. If the header or headers are present, Internet Explorer does not cache the file. Consequently, Office cannot open the file.
RESOLUTION
Web sites that want to allow this type of operation should remove the no-cache header or headers.
STATUS
This behavior is by design.

Hope that helps,

Ten Pentacles

I'm afraid this doesn't help: openrdf.org does not communicate over SSL.

OK then it is more than likely a config issue with the particular user.

I had the same problem a few days later. Here are the case notes and solution. Best part of is that you can reproduce the error to prove it is the users config.(see below)

PROBLEM:
When a user tries to download files they receive the below error. The error is not related to a specific file type, server or site. For Example, it is possible to download a document from one @hp site, but not another, and or from a site like CNet, but not Microsoft.
Error Message:
Internet Explorer cannot download "filename" from "Servername"
Internet Explorer was not able to open this Internet site.
The requested site is either unavailable or cannot be found. Please try again.

====================================================

SOLUTION:
Internet Explorer-> Tools menu-> Internet Options-> Advanced tab
Go to the Security section all the way at the bottom.
Clear the check on the "Do not save encrypted pages to disk"
Close all Internet Explorer windows
Start IE and download the file again

That should to it.

Hope this helps,

Ten Pentacles

I just had this issue pop up after months of everything working okay. Hours of mining google results turned up a different problem with another basic fix. 'Fraid I didn't capture where I found this to credit them...

Open Internet Explorer. On the Tools menu, click Internet Options.
2. On the General tab, under Temporary Internet files, click Delete Files.
3. In the Delete Files dialog box that appears, click OK.
4. Under History, click Clear History.
5. In the dialog box that appears, click OK.
6. Quit Internet Explorer.
7. Log on to the computer by using the account of a user who does not experience the problem, and then open a command prompt.
8. Change the directory to the following path:
drive:\Documents and Settings\username\Local Settings\Temporary Internet Files\Content.IE5
where username is the name of the user account that has the problem.
9. Type del index.dat, and then press ENTER.
10. Close the command prompt, and then restart the computer.
The Index.dat file is recreated the next time that you log on to the computer.

I currently have this same issue with my computer. Another problem that may be in connection with this error, is when you open your history in IE, nothing will appear, whether you've gone to a website or not. Also, there is the inefficiency of cookies. Any website you have cookies on (such as to remember your username/password), you will have to login by yourself, and often times unsuccessfully at that.

I've read the first solution which doesn't help my case, and the second solution becomes too complex at step 8 and I don't have another user account.

I had this problem with downloading online "bills" from two web sites using IE8.
Thank you very much "Ten Pentacles" -
your solution to "Clear the check on the "Do not save encrypted pages to disk" was succesful.