Hi Bob,
Thanks for the basics, I appreciate that. There are three ways of connecting the USB to the Airport Extreme network as a network shared drive. Under the OS X Mavericks I was able to connect USB to the network using a "disk password" option. That stopped working under the OS X Yosemite. I was now able to connect the USB stick using "an account with password" option, so far so good. However, that option only works when I create a new account (not using my default administrator account). I can connect the USB as a networking drive via the Airport Extreme using that other than default account and I see two folders appearing on the networking drive: one goes by the name of the USB stick and the other by the name of the new account. Within a few seconds, however, the folder that goes by the name of the new account changes its name to the default account (i.e. my administrator account). One would think that he has just overcome the problem, but in every new session (after a fresh start of the MacBook Air, server/router, ..., and everything there is) I have to repeat the steps outlined above, the network does not remember the last successful connection of the USB as the networking drive. The network does, though, remember the settings for the new account I have created before. But whenever I try to connect the USB stick under a new session (fresh start of everything ...) I have to connect that USB stick to the network under that different non-administrator account, and again within seconds the name of the account/folder changes to my administrator account.
That only happens on my Mac (MacBook Air). My PC with Windows 7 which is also connected to my network, uses the new account only (logically) and sees the networking drive right from the start. The PC remembers the settings and whenever I start it anew it connects automatically to the networking drive.
Your helpful comments and advise will be much appreciated.
Thanks, Zed