Hi All,
Don't know if this would be helpfull, it looks like the same problem when i configured my Raspberry Pi for XBMC for the first time. I also had problems with the NFS share permissions.
In the following link there is a explenation how to configure NFS for Synology in combination with XBMC (needs some editing in a config file).
http://www.robvanhamersveld.nl/2012/12/ ... -with-nfs/
Hope it helps, it did the trick for me .
Greetz