Marco Russo takes us through an issue with naming in DAX:
You deploy this model and start creating reports using the Sales Returning Customers measure. So far, so good. One day, you need to extend the data model importing a new table that you decide to name ReturningCustomers. As soon as you import the new table named ReturningCustomers, your measure Sales Returning Customers stops working. The reason is that the ReturningCustomers variable generates a name conflict with the table that has the same name, as you can see from the error message.
‘ReturningCustomers’ is a table name and cannot be used to define a variable.
Marco has some advice if you’re in a situation where you are liable to see this pop up.