Hi Eveyjoy, 

I have been getting the same issue when the tax is set to "Based On Location" all day. It is a new occurrence and QBO people on the web in forums are noticing the same. I am assuming its a software anomaly.

Fix for me: I manually changed the tax to the "State Tax" and sent it directly. If I try to save and then wait and send it, the invoice automatically shifts bac to "Based On Location" and it will create an error. 

If you are sending it, I would use another tax option and then go right to 'save &send' until QBO can resolve the problem. (It is ironic since none of the invoices I sent out today even had a taxable charge on the invoice.) They still failed on tax calculations when the invoice reverted back to 'Based on location'.