Ok, due to our mailinglist a lot of traffic was going to our server, and the windows2003 application went belly up. My ISP's helpdesk at night is formed by people who never saw a website nor computer, so it took me 3 hours to get to a sysadmin who restarted the webservice and it works now again.
Apparently we need more bandwidth/memory. Will be added first thing in the morning.
. It appears the website leaks memory (but I don't know why, the code hasn't been changed in months) and it then hits the apppool limit. Could be the downloads which add to the memory pool. I hope we can keep it up till the morning.