Power BI - teams

Hi 

I am having trouble showing a report in Teams that has been created in power BI using an excel datasource in Teams. When I try to create a tab to visualise the report from Power BI I am getting the error message - Unable to save configuration for "Power BI" tab.

I am new to Power BI but I have managed to get this function working previously so not sure what I am doing differently. Any ideas?