Sorry for the delay. Looks like you do not have title set for this page.
http://www.testbetrieb.info/germann/?page_id=5246
or you removed it by changing the value of header options in the page edit window. Can you pls set the page title and pls post a temp login here as a private message in case you still have trouble.
Regarding the home page portfolio having empty items, you need to have post_count set in such a way that the system is able to pull items for from all categories. So, pls modify the portfolio page section to have the post_count in the shortcode below to higher than 8 like this (like 12) depending on number of portfolio items you have –
[show_portfolio number_of_columns=4 post_count=12 image_size='medium' no_margin=true]
Hope this helps.