Where is the error when electronic filing fails? The email says "Once you've opened your return in TurboTax, the details about what needs updating will be displayed."

Under "What Happened" it says: "/Return/ReturnData/IRS1116/ForeignTaxCreditSource/USTaxWithheldOnDividendAmt - Data in the return is missing or invalid." But Form 1116 is very complicated, and there is no explanation in TurboTax what is wrong with the form.