Macbook Isn't syncing photos correctly? Help please

Hi,

I am having some trouble with synching photos to my macbook. It starts off fine, however once the process has 'completed' only 100 out of my 900 photos have sync'd and the pictures that have sync'd have been messed up. An error messge pops up saying that the downloading of pictures has not been successful.

Has anyone had this problem before? Does anybody know what this might be and how I can fix it?

Thank you,

Maria.