Downloading Files / Asp-error With ZIPs Only

I have the following problem:

working on a "downlad-module" within a larger website, i tried several methods for downloading-files to the user.

mabye some basic infos first:

the website runs on win server 2003, using sql server 2000-database; pages are written in classic asp. The idea behind is, that all possible download-files (flyers, brochures, some it-stuff.. means pdf, docs, exe, zip-files.. "standard-mixed-stuff, i would say) are of course stored outside the website-root and are uploaded using a cms.
for each file, the information is stored in a database (not the file itself). beside path and filename, also content-type, descriptiton, user-restrictions etc.

within the page, the user will than receive a list of possible download files.
by clicking on the link, i redirect to a "download.asp"-page, where i just want to start the download by sending the file to the user. so far - so bad :-)

i tried 2 free components (TabsUpload; aspSmartUpload)and also a simple response.BinaryWrite and here´s the problem: everything works fine, as long as i am messing round with other file formats than ZIP (!). I can use the system for downloading pdfs, exe, docs... but when i want to dl a zip-file, the system "hangs up" (only the browser wants to connect endlessly.. its not a crash, because i can stop it by using ESC-key)

one interesting thing:
when i use the the BinaryWrite-method, a file is downloaded - but of course not the zip file - it is a html-page with the wrong content-type ;-) using a text/hex-editor, you can find this error message: Response Buffer Limit Exceeded

possible solution for this would normaly be, to turn Response.Buffer = False
but, for using either binaryWrite or one of the components, Response.Buffer should be set to True, as far as i know...

so anyway, here is the source-code: ...