As described in other threads, I filed a 4868 to make a $5K over-payment, to be refunded as IBonds. And did it all through freefilefillableforms.com
In filing the online 4868, part of the form gives a bank routing number and account number for the payment, and a date on which to make the payment. So that was all submitted just fine.
After the payment had been pulled from the bank account, I went back and filed the 1040. After a few hours I checked back for status and got an error report "The XML data has failed schema validation." The additional information given was "/efile:Return/efile:ReturnData/efile:IRSPayment/efile:RequestedPaymentDate" How descriptive of the error!!!
For the benefit of anyone who encounters this same problem....it was the form 4868 that was still included in my tax return that caused the problem. The payment date on that form was in the past, of course. Didn't they know that the 4868 had already been filed?
Fix: delete the form 4868, and re-file the 1040. Went through just fine.
Hope this helps anyone else that gets this strange error response.