OK the "family tree" directory on the freenas box needs special attention .. fstab doesn't like spaces in filenames, so you have to replace them with the special octal character \040 .. so family tree becomes family\040tree
add a NEW LINE at the bottom that reads:
//192.168.2.100/family\040tree /mnt/freenas/family-tree cifs credentials=/home/graeme/.smbcredentials,iocharset=utf8,dir_mode=0777,file_mode=0777 0 0
SAVE the file.
Check the family-tree folder (in NAS on desktop) .. can you see the files ?
If this works .. be sure to read my next reply BEFORE rebooting