Bitcoin-qt data on external drive I have done the instructions listed here:
How to move Bitcoin data from Application Support on an external drive [Mac]

It works fine for a flash drive connected the mac, but I wanted to have the data read from my network storage device (ReadyNAS). Bitcoin-qt comes up with the following error when I link it to the NAS:

EXCEPTION: N5boost12interprocess22interprocess_exceptionE       
Operation not supported       
bitcoin in Runaway exception 


Any ideas on what this could be?
It is trying to acquire a lock on the lockfile in the data directory, which likely fails due to not being supported on the network file system you use to access your NAS.

Even if that could be safely ignored (the lockfile is just there to prevent you from running multiple Bitcoin Core instances on the same directory), it is a warning that more problems exist. In general, running a database on a network filesystem is a bad idea because of lack of support for operations or guarantees that databases require. It would either just not work, be very slow, or get corrupted very easily.

However, this is all because of the databases used (blocks/ index/, chainstate/ and wallet.dat). The block data itself is not a database, and could be moved elsewhere. Bitcoin Core does currently not support moving just the block data elsewhere, though.