thank you for answering so quickly
I use to the mac os x "el capitan" 10.11.1 and the lightroom cc 2015 v.1014445. the files are in the cataloge and I think they are properly linked.
Please try and turn off the Graphics Processor and see if that helps.
Go to Lightroom Preferences
Click on the Performance tab
Uncheck the Graphics Processor
I try turn off the Graphics processor, as you said but it did not work , I'm having the same problem. I tried reinstalling the lightroom but the problem remains , as if that were not enough now tells me that there has been an error saving metadata " Could not write metadata. Error I / S unknown file "