To fix this:

Clear cache and cookies. Then once cache and cookies is cleared, close completely out of the browser you are using, and relaunch.
In the browser you’re using this can usually be found under, settings, advanced setting, then “Clear cache and cookies.” When you do this you want to change the time frame of the clear to “all time” so you can start fresh.

Some additional troubleshooting that can be done:

• Make sure your operating system is up to date.

• Make sure you’ve rebooted after you had any updates

• Try different browsers. Chrome, Firefox, Edge, IE, Brave.
  

Please see the following Turbotax FAQ for more information: https://ttlc.intuit.com/replies/3300688

Did you ever fix this? 

Not helpful. 

I've tried clearing cookies, new browser etc. No dice.

I found a possible solution.  I'm not sure if it will work

TurboTax Help 601ERRV...

Although Turbo Tax recommended I clear my cache and cookies that did not resolve the issue.  After reviewing my state returns multiple times I discovered I duplicated an entry within one state return - per the error code I emphasized with Turbo Tax (see error code below) .  VA taxes you on income tax from other state(s) income but you can go in and claim each state separately within VA's state filing to eliminate being taxed twice.  I apparently had duplicated a state twice and I believe that was causing the error.  I believe this because I was able to individually submit all my other returns but could not do so with VA.  Needless to say I've spent far too much time on something that the Turbo Tax audit system should have caught and if not Turbo Tax Customer Assistance.  Disappointed in Turbo Tax given this is the first time in 13 years I've really needed their assistance and they couldn't seem to assist.  The default response was you may have to file by mail.  

Error message after attempting to transmit: We are having difficulty recognizing the data you are sending. Please try again.

:?, FilingHdr_41.1 - ?:? - Duplicate attachment name detected '/attachment//DEStateReturn.pdf'