installer corrupted?

I downloaded client 1-13-2-15 about 20 or 30 times now, with and without Firewall, directly from the homepage or by starting the old client, letting him update - well, letting him try to update. Every time I get the same error:

"The installer you are trying to use is corrupted or incomplete.
This could be the result of a damaged disk, a failed download or a virus.
You may want to contact the author of this installer to obtain a new copy."

Has anyone an idea how to fix this?

Disable firewall / something else you might have, that could corrupt the download.... SL still have only one download place (wich seems to been capped in download speed now blergh), otherwise i would have suggested another place to download it from.

I now used another computer (that I first had to assemble), burned the client to a CD and read it in on my main computer.
That works for now, but I would appreciate if I hadn't to do this for every update

As I wrote above, I had disabled all firewalls, except the one in the router. Since it worked with the other computer and the same router, this doesn't seem to be the problem's source.