In shopthankslinks.asp the secure download links sent to e-mail are generated incorrectly and cause the links to not work for downloading files. This bug effects 6.50.4 (from comments in the file). To correct the bug do the following:
About line 301 you will see the following code:
url=getconfig("xmysite") & filename & "&cid=" & customerid
Replace this line with the following code
url=getconfig("xmysite") & filename
The problem is that the cid variable gets added onto the querystring in two places, line 286 and 301. Download links displayed on the shopthankslinks.asp page are not affected, only the e-mailed links.