at what point does this occur? Can you Convert only, without transmitting?

Have you verified your PTIN - it's a new step this year.    Tools>Options>Firm/Preparer Info    look for pink colored check box near your PTIN#

Hi Lisa, Yes I can convert only. I did that but when I tried to transmit it, it says it appears you are trying to transmit a return that has already been transmitted. Like a duplicate social security, I have not called the taxpayer back to ask them if something happened, trying to figure out if there is a problem with the system. I have prepared returns after that problem and the software seems to be working just fine. Thank you. 

If it tells you a return has already been transmitted, it could be that someone else (not you) using an Intuit product (even TurboTax) has filed a return for that SSN.