Sum column values based on another table

It is because of relationships are not appropriately defined in your model. Looking at your model, it seems like you need to make the following changes: 

- Change Relationship between Table1 and Calendar to be Many-to-One and Single-Directional. (Note the Many should be from Table1). 

- Change Relationship between Table2 and Calendar to be Many-to-One and Single-Directional. Then ensure that the relationship is active. (Again note that Table2 should be many side.)

- Create new relationship between Table2[Office] and Offices[Office] as Many-To-One and Single-Directional.

- Change the measure TotalExpense = SUM(Table2[Expense]). It is possible that I misunderstand the requirement for this measure. But it is good to start simple and then define a more complex measure if needed.

I tried these changes and seem to be getting the correct numbers, but you should verify if that is what you want.