I just upgraded to 6.4 on my 1197 and when I hit "mark" I get the "sad sound" and it says "successfully saved" but no waypoint is created. On my 957C the 6.4 upgrade worked fine, and I can created waypoints.
I have a bunch of Interlink issues too, but I can't worry about them until the create waypoint issue is resolved. They may be related, because on the 957C I erased the Interlink, and merged the data, and it worked fine. It saw the 1197, and read the correct number of waypoints on it and on the 1197.
But the 1197 is a mess - can't create waypoints, can't sync the Interlink, and so on. I've tried disconnecting the Interlink entirely and still can't create waypoints.