Thanks for your reply.
Yes I did remove the datebase as well as all my photos in the picture directory and let shotwell reload my photos from back up. It crashed again. after a few thousand photos had been copied.
Fed up I downloaded f-spot and let it load my photos from backup I let f-spot copy my photos back into my picture directory. However I noted that f-spot crashed as well but not until it had copied my photos till the year 2013, so only the last 8 months hadn't been copied.
I then run a brand new installation of shotwell again and it updated its datebase fine from my photos in the picture subdirectory - it didn't crash. I figured that something was wrong with my photos in the year 2014, so I added a month at the time. Shotwell crashed again when I added the month of May. When I checked my photos in that month I found 2 video files had been copied there - mp4 files with nothing on it - I have no idea where these video files come from or how they had got unto my computer, but somehow they got there. I deleted the files and then added all my photos of 2014, Shotwell loaded and updated fine and is up and running fine again.