Problem using Power BI Service as data source

I have problems using Power BI Service as data source.

I created a blank pbix-File with some sample data via Enter Data and published it to the service.

When I try to use this as data via Get Data>Power BI Service in a new pbis-File I get this error message:

Unexpected Error,

An error occured while loading the model for the item or data source xxx. Verify that the connection information is correct and that you have perissions to access the data source.

I have no idea how to fix this. When I try this in a complete new PowerBI free account it works.

Any idea which mistake I made?

Thank you

Andreas