Apple recently introduce a new feature called "Journaling." This has caused some problems with transfering files to the units using the Apple File Sharing protocol.
As a temporary fix, you must make sure that the character names are no more than 32 characters long, and that the following characters are not used:
* / \ : < > “ | -
Also, you may disable AFP in the NAS and use SMB to connect.
To connect using SMB, go to GO > Connect to Server... and type in smb://ip-string-of-nas or smb://nas (where nas is the name of the NAS, assuming you did not change it).
If you still experience problems, you can connect using FTP to the NAS as the protocol.
Tritton Technologies will continue to work on this problem and post a permanent solution when we find one.