What are "nwnode:" URLs, and why did Lion break them?
The error occurs when an application using Python symbol mappings in Mac OS X is not able to connect to a (previously) networked drive, Time Machine, Bonjour, shared or remote drives, etc. (nwnode). It's a depreciated method, which mostly is why Lion displays the error. Even if you don't use Time Machine, this error can occur, either from an os upgrade or app that uses Python (Dropbox in this case).

Usually the issues can be resolved by following these steps (via Apple): 

Resolution


In the Finder, double-click on your hard disk.
Open the folder named System.
Open the Library folder.
Open the Filesystems folder.
Drag the folder named "URLMount (from old Mac)" to your desktop as a precautionary backup.
Once the copy is complete, control-click the original "URLMount (from old Mac)" folder (not the one on your desktop) and choose "Move
to Trash" from the contextual menu.
Enter the name and password of an administrator if prompted. The first user account created on your Mac is an administrator account.
Restart.


http://support.apple.com/kb/TS1736

*note: The question above was posted six months ago, although I decided to answer it today simply because nobody seemed to know the answer. Hopefully someone who reads this will understand what the error means now.

And just for Bryson, here is just one of it's strings in symbol_mappings.py:

'__ZN17SharePointBrowser18setConnectionStateE21NWNodeConnectionState' :
 'SharePointBrowser.o',