Error deleting a waypoint file

I have been using the PC at home to create Waypoint files (about 1,000 waypoints in the Gulf of Mexico). It has been working fine up to this last week. I have three waypoint GPX files stored on a compatible SD card with different labels. I go into the DATA screen, select the current waypoint file on the system and try to delete all 1,000 waypoints and it responds with an error. Can you give me a clue what I am doing wrong. I also tried to delete the waypoint file from the CHART - WAYPOINT pull down menu.

Thanks for any advice