@Deni_Ribicic
thank you very much for your quick and helpful answer. 
Creating the metadata file worked. I started with the example file from the Metadata Tutorial. Consequently, the creation of the barplots has now worked.
The correct display with iTol now also works. If you insert the files 10..., 11... and 6.2... according to the thread Loading Greengenes tree in iTOL it works.