Hi Martin,
Thanks for contacting Syncfusion support.
We are unable to reproduce the mentioned issue and it’s working fine with our IIS server. We have prepared a runnable sample based on this and it can be downloaded from below location,
http://www.syncfusion.com/downloads/support/forum/121119/ze/ReportExportDemo898444123.zip
For your reference, we have deployed the above sample in our live server and please find the hosted sample link below,
http://ssrs.syncfusion.com/ReportExport
If the issue still persist, please share the reproducible sample with us to validate the issue?.
Regards,
Soundara Rajan S.