If you get the error "Name can't be blank" when saving your estimate or invoice in Joist, take a look through your line items and check to make sure each one has something entered in the "Name" field.
Here's an example:
It's easy to miss sometimes, especially if you have entered information in the "Description" field. It's ok for the "Description" to be blank, but the line item always has to have something entered in the "Name" field before the estimate or invoice can be saved.
Once you've made that change, try saving again and you should be good to go!