Why does Franchise tax board cannot process my amended return? Are they not expert to determine the eligibility for amended return?

TurboTax receives no information from the state after you file your tax return, so no one at TT knows what the state changed or why they now say that you owe.  Apparently they believe you made a mistake, but no one at TurboTax can say what it was.   Only the state can explain it to you.

Was the 403 the tax due on the original state return?   You do need to pay that.  Then the amended return is for the difference you get back.   The amended return assumes you paid the first tax due.