This is a browser window issue ... try using the incognito option.
You will need to contact Costco.
Go to this website for contact information - https://techsupport.costco.com/app/answers/detail/a_id/1001266
I found the easiest way to fix the problem. What you need is an account on turbotax.com. One signed in, click on download, then enter the activation key furnished by Costco. After that just follow the instructions on the screen. Worked for me.