This worked for me, you give it a try:
If unlinking and relinking your account doesn't solve the issue, your settings may be protected or inaccessible due to a permissions problem. If this is the case, you can remove your settings by hand using an administrative account. Here's how:
- Quit Dropbox by right-clicking on the Dropbox menu from the menu bar and selecting Quit
Open a terminal and copy and paste the following line into the terminal (exactly as written below):
sudo rm -rfI ~/.dropbox
You will be asked for your password to confirm the folder's removal
Restart Dropbox from the Applications > Internet menu
Once Dropbox loads, the application will rebuild your settings files and you will be asked to relink to your account.
Note: We're working on a way to check and fix your Dropbox installation automatically from within the application. Stay tuned...
(From the Dropbox Help Forum Team)