The pretest URL seems invalid, please see the manual for how to create a valid pretest URL.
> How can I find out or change that i can download two files from a server at the same time?
Open the developer tools in your browser, please. Then open the "network" tab. Only then load the page - and look what the network information says about the files.
If one is blocked, it's likely a limitation by the server.
You will not be able to change that at all. That's a server setting. What you can do is ask the IT guys if they can remove the limit.