[26 March 2016] Dropbox changed something :-(
There is currently an issue with Dropbox syncing and uploading which affects some users.
The 'fix' is as follows:
Goto the System Settings section in the iThoughts app, scroll to the bottom and switch the 'Dropbox app auth' to OFF as below:
Then goto the Share toolbar button (rightmost) and choose the Cloud -> Cloud Accounts -> Dropbox option then Save/Login as below:
You will be prompted for your Dropbox user/password. Once you have been (re)authenticated everything should start working again.
Apologies for this - I am investigating why it suddenly started happening.