Hi Rene Massy,
Thanks for using Syncfusion products.
We hereby inform you that when our BI Client ASP.NET is placed under master page, we would recommend you to set ClientIDMode to "AutoID". Here is the code snippet.
[ASPX]
<cc1:OlapClient ID="OlapClient1" ClientIDMode="AutoID" runat="server" Height="600px" Width="800px" />
Please let us know if you require any further assistance.
Thanks,
E.Hari Venkatesh