yes there was a problem with a plugin
I’m German, so I had use a plugin, that called wp-permalauts, that makes for us, german user, easier to read the permalinks. This plugin changes the charakters from ü=>ue, ä=>ae, ö=>oe, ß=>ss, and so on, I deactivated this plugin and rebuild the permalinks, and there it works.
Thaks a lot
Best regards Rico