My son's fed and state tax are being rejected. He is filing married separate. His wife left on 9/26/18 and remarried 03/15/19. Why is her ss# needed? We tried with her ma

[SweetieJean]

Did they live in a Community Property State? If so, that complicates filing MFS.

[SweetieJean]

"His wife left on 9/26/18 and remarried 03/15/19."
Was the divorce final in 2018, or in 2019?

[DDollar]

When married and filing separate, the IRS requires the taxpayer to include the social security number of their spouse on the tax return.  Their are special rules that apply to these tax payers, for instance, if one spouse itemizes then the other spouse must itemize as well (cannot take the Standard Deduction).  The IRS matches up information for the two.