This also gives an invalid argument. I'll stop here for now, as I have to take care for the kids. I'll try again tomorrow or later on. It might be, that the mount point sdb1, as beeing created by udev rules atm is causing trouble. So I will go back to stock version ov the udev rule, create mouhnt point by hand and try to use the recommended arguments.
Thanks for your help by now. It is always a pleasure to find helpful people on the web!