When you try to import , drive crashes or you wanted to say that lightroom crashes ?
No the access to NAS crashes. You can work with all the photos stored on there but not import
When did you upgrade to El Capitan? Recently?
When it was released, so some time ago.
Then start with running some diagnostic on the NAS. Could be there is a failed or failing drive in your NAS. That is if it has multiple drives. You should be able to log into it through a web browser using the IP address of the NAS to view the built in webpage and see if any errors, problems, are being reported.
I see there is special software for that NetGear device. Check that to see if there are any problems with the box.
That was the first place I checked. No disc issues or access is set for Read/Write; all as it was before LRCC