browser cannot readt html if it is on server

Dear community,

a few months ago I found the programm Lumi and I was so glad for the possibility to convert H5P files in html. I wantet to integrate H5P content to our online library, so I put the html file on our server. But when I try to open the file with the browser, it just shows the kryptic source code. I can open the file without any problems with every browser on every device, as long as the file is on the device itself. As soon as it is on the server, the graphic representation fales. 

Does anyone know what could be the problem? Is it a server-thing?

Thank you!