Upload aborted with timeout

Hello NG, for some reason we have problems with midsize to big file-uploads (around 5MB and bigger) that are performed by the website-visitors. It most likely ends in a time out (60 sec), even though the internet-connection is sufficiant (server AND client). We already tried everything (known to us): - set max_execution_time to 1 hour - post_max_size = 50M - upload_max_filesize = 50M - ... None of these parameters seems to have an effect on the system!? At another point I read that there might be parameters for the webserver iis to set for execution? Thankful for any hint .. Marc