Thank you very much 
I did another take with the Process Monitor and found something i missed before.
When developing the webpage, i assigned a fixed path to the CrystalReportSource, which i thought would be ignored since the first thing my sourcecode would do would be to load another document.
But it still tried to load that Report with my local path and didn't even get to loading the specified report.
Now that i changed that local path it works.