Called technical support (on hold for over 2 hours). They're aware of this problem...a "glitch in the system". To verify if the return was submitted correctly, go to your home base and check the amount of your clients refund after it was accepted. If it's the same amount as on the return when transmitted, then you can ignore the error message and no amended return needs to be filed.

I asked if they would be posting an update once the issue has been corrected and was told "no, it will just go away". This is to serious of an issue not post an update about it. Some preparers may file amended returns unnecessarily.