why in the past was i able to do multiple returns - Because you were probably using the TurboTax desktop CD/Download editions where you can complete as many tax return as needed.
You are using the TurboTax online editions which can only be used for one tax return per account and User ID. To start another return using the online editions you will need to create a new account with a new User ID.
https://turbotax.intuit.com/personal-taxes/online/
