Project Online Pro Client add Tasks to MS Planner 'Cannot Create Link...'

Hello, 

We've recently established a Project Online Web App and have some demo projects published.  We are working through syncing Project tasks to Planner.  To do this we are using Project Online Pro and working in the client application. 

We keep getting a 'Cannot create link...' error message.  We've searched and tried a few things but still no luck.  

Has anyone else seen this?  Or can anyone provide links to troubleshooting resources? 

Thanks.