Direct Query to Power BI Dataset no longer working

I have a report which had a direct query to one of my power bi datasets that is stored on a workspace on the Power BI service which has been working for two months and has suddenly stopped connecting. If I try and reconnect to the dataset, I am presented with an error message below. There have been no changes to permissions in the workspace.

What confuses me, is that if I open a blank PBI Destop and connect to the same Dataset it connects with no problem. I have checked the settings in my existing PBI report and a new blank version and they match.

Any ideas as to what this could be?

Many thanks.