This is a spontaneous connectivity issue that usually resolves itself if your connection to TurboTax remains intact while the process you are working on completes.
If the issue doesn't resolve on its own, close TurboTax, restart your computer, and reopen TurboTax.
If that does not solve your problem, consider some other things you can try:
Reset your wireless access point and try logging in again
Turn off your computer, your router, and your cable modem, in that order
Wait a minute, then turn your modem back on
Wait another minute, then turn your router back on
Once your router is back up, turn your computer back on and try logging in again