I have several libraries in iPhoto. I would like to move to an external drive. I have successfully EXPORTED some of the libraries to an NAS drive. Am having trouble with one library. It will export over about 25-30% of the pictures then stop and give the following: UNABLE TO CREATE/USERS/XXXXXX/XXX (am using Xs instead of the real path name etc.)

Always stops at the same point when I retry.

How can I get rid of this and get past this error message?