Mavericks includes the new SMB driver SMBX2, which is supposed to fully implement the SMB2 and SMB3 protocol. Unfortunately it has been reported that SMBX2 is not compatible with many NAS products, and some older Windows servers (example: Windows Server 2008 prior to R2).
Fortunately, Apple included the older SMBX driver in Mavericks, and you can connect to SMB shares using it instead of SMBX2.
If you are having problems accessing an SMB share with Mavericks, connect to the share using cifs:// instead of smb://
HISTORY: Because of GPLv3 licensing conflicts with Samba, Apple was forced to write a SMB driver from scratch when they released OS X 10.7. This driver was named SMBX, and was used with both OS X 10.7 and 10.8. It only included the SMB1 protocol.