Suddenly getting a "not supported" error when trying to add Phone Call to wall

Until recently, I have been using Dynamics Sales to track calls to leads, by manually adding a call on the ‘wall’ for the lead or opportunity.

 This week, the feature seems to have stopped working. I now get this when I click on “call”: 

An error has occurred. Try this action again. If the problem continues, check the Microsoft Dynamics 365 Community for solutions or contact your organization's Microsoft Dynamics 365 Administrator. Finally, you can contact Microsoft Support.

Error code: 0x80040315

Session Id: 55782ca6-dfd3-451a-abc2-18a7fa609a58

Activity Id: bb64f60d-eeab-4179-b6d7-42481e35245e

I have asked our admin about any changes, but they have nothing that would explain this. The feature also continues to work for other users in the organization. 

Does anyone know what this might be?

Thanks in advance, 

GP