You may be unable to duplicate a Project for 2 reasons:
You have reached your Project limit
You are trying to duplicate a Project which contains Categories that are unticked from your library
Reached your project limit
If you have reached your project limit, you will need to upgrade your account. You can do this by going to Settings > Billing and choosing to upgrade to the next package. Alternatively, you can email help@handshq.com for assistance.
Category unavailable
If you are seeing the error message above when you go to duplicate a Project, this is because the Project contains a Category that has since been unticked from your library.
If you click into the Project, you will be able to see that the Category will now appear at the bottom of the list and will display as 'Unavailable'
In order to resolve this, simply go to 'Settings' on the top right-hand side of the account, scroll down and ensure that all the Categories used in the Project are ticked.