RESOLVED!
I ran into the same problem, and finally found a work-around that allowed me to transmit:
1. Delete CA return and start over using the instructions via the following link:
https://ttlc.intuit.com/community/state-taxes/help/how-do-i-clear-my-state-return-in-the-turbotax-fo...
2. Start the new CA return fresh. HOWEVER, immediately after the first couple of screens where you verify company info, and BEFORE getting to the screen where you enter how much tax you've already paid, you select FORMS in the top-right, then choose Form 5806 in the left navigation area, to display the form, THEN CHECK BOX B in the large framed box near the top with the title "Form 5806 Smart Worksheet". When you check Box B, with description "Check this box if you want the FTB to calculate the underpayment penalty for this corporation. Form 5806 will not calculate", you'll notice the remaining fields are all blanked out.
3. Click on the Step-by-step icon in the top right, and continue with your CA return.
You should have no issues with that form after that!
Mike
