You will need to keep the ethernet cable plugged-in. The catalog must be on a drive on the Mac and not on the NAS with the images. If you loose connection, you can’t edit photos. It’s one of the drawbacks of using a NAS/RAID system. An external hard drive is really preferable imho. Even they can fail; so good back-up is essential.
Use the Organizer to catalog and search for your photos that are stored on the network. When connected to the network, once you've found the photos you want to edit offline, highlight them in Organizer and use File...Export as New File(s) to copy them into a working directory on your notebook. You can then open them directly in the Editor for processing whether or not you're connected to the network. When you're next connected to the network, use a tool such as MS' SyncToy to synchronize the photos in your working directory up to the network. In Organizer, you'll need to select the photos again and use Edit...Update Thumbnails.
That's a tedious process, for sure, but no matter where your photos are stored (CD, external HDD, network drive) you can't open them for editing from the Organizer if the storage location is not connected.
You do not understand my problem right. My fotos on the NAS are my old pictures taken over years and saved in old style manner, one directory per event, without using any software. Now I bought new notebook dedicated to foto processing (with 1 TB disk installed), I installed Elements and I would like to execute this two operations, copy files and first time import into catalog, in one step. I do not understand, why I have to exit Elements when importing my files into catalog, the option 'Copy on Import' is exactly what I need. I do not see any reason for the grayed out checkbox.
In that case simply drag and drop all the folders into My Pictures on the notebook C drive. When everything is on the hard drive click File à Get Photos & Videos à From Files & Folders
Then navigate to My Pictures, make sure all sub folders is checked and click Open or Get Media.
Select all suggested keyword tags and wait for elements to generate thumbnails.