Where is the shared folder in Remmina?
As mentioned above, it's working for me with Remmina 1.2. The shared folder is available at \\tsclient\<SHARED_FOLDER_NAME> (in case it saves anyone any time looking for it).
In older versions of remmina there were some bugs, please ensure that you have recent version (like 1.2.X).
You may want to use remmina-next to get it:
sudo apt-add-repository ppa:remmina-ppa-team/remmina-next
sudo apt-get update
sudo apt-get install libfreerdp-plugins-standard remmina remmina-plugin-rdp