OK, in a nutshell, if you get the 1116 error for the attachment, the file name must be Form1116ScheduleB, and make all pages into 1 attachment.  Solves the issue every time😎

From the reject...

"If Form 1116, 'ForeignTaxCrCarrybackOrOverAmt' has a non-zero value, then a binary attachment with description 'Form1116ScheduleB' must be attached to 'ForeignTaxCrCarrybackOrOverAmt' and 'ForeignIncmSection951AInd' must not be checked."