Confirm that you have a good internet connection. Hardwired connections work best. Try not to have other programs running in the background or multiple tabs open when you are trying to submit. Try turning off your router and turning it back on, exiting and reentering the program, and then try again to transmit your return.
If you confirmed that all of the procedural steps were followed, you have a good connection, and you still get the transmission error message, please click here for information to contact TurboTax customer support.