It is working now. This is what I did. You probably won't need all these steps to make it work but just to be sure try them all:
Check the account parameters of your scheduled task and make sure they are set to run whether or not someone is logged into the machine
check run with most privileges/rights
Make sure you go to the full path first: cd C:\inetpub\wwwroot\infoweb\factuur\cron
Don't use double quotes in your batch files (don't know why but seems to help)
Be super admin, enter 'Net user administrator /active:yes' in command prompt, log out and log in as the super admin, so UAC is off