I had this issue, too. Regardless of the idiocy of not changing the estimated tax payment deadlines to match the return deadline, it is seriously stupid either (a) that the IRS does not allow scheduling the payments on other dates, even if they are past due, like this is some feat of extraordinary technology beyond our capabilities; OR (b) if it is not an IRS rule, that the software does not allow such scheduling, again, as if it is beyond their programming abilities. It is also seriously stupid that the only solutions that anyone can find are either to not schedule the payments at all or to double up the second payment in June. And, thanks for the helpful error message....