Cannot Sync Brand New DataMart

Just created a New Datamart, connected to an Excek=l file in OD and brought in 4 tables from there. All looked good.

But if I refresh in the "Transform Data" screenb it shows any changes I have made to that Excel file since the creation of the DM ... minutes later.

But this new info does not ripple back down to the main DataMart tables and if I try to refresh the DM I get this message: