David,
This may happen due to duplicate Contact Groups. See attached image.
dup contact group.JPG
In that case what you need to do --
1. Go to Clients and Contacts group and activate the Contacts tab.
2. Click ‘Manage Contact Group’.
3. In ‘Manage Contact Group’ dialog check if you have a duplicate contact group.
4. Edit the dup contact group to a unique name.
Let me know if this helps.