I'm sorry for your loss.
When a tax filer passes away during the tax year, one of the responsibilities of whoever handles the final affairs (usually the funeral home) is to notify the Social Security Administration of their passing. Upon notification the SSA will lock the SSN of the deceased so it can't be used fraudulently.
Every year around the end of December or first part of January the IRS pulls taxpayer information from the SSA computers. In the case of a locked SSN, the IRS computers will also lock that SSN so that it can't be used on *ANY* tax return that is filed electronically, forcing the preparer of that tax return to mail it. The most common error code from the IRS for this is "SSN LOCKED". But it could be anything.
In cases like this, you have no choice but to print, sign and mail the return to the IRS. additionally, if a refund is due you may also have to include IRS Form 1310 so that the IRS will not put the name of the deceased on the refund check. Instead, they will put the name of the person who has proven to the IRS that they are entitled to receive the refund of that deceased taxpayer. You can get the IRS Form 1310 at https://www.irs.gov/pub/irs-pdf/f1310.pdf if you need it.
To see if you need to include IRS Form 1310 with your mailed tax return, see IRS Publication 559, page 4 at https://www.irs.gov/pub/irs-pdf/p559.pdf. It states:
If a personal representative has been appointed, that person must sign the return. If it is a joint return, the surviving spouse must also sign it. If no personal representative has been appointed, the surviving spouse (on a joint return) signs the return and writes in the signature area “Filing as surviving spouse.” If no personal representative has been appointed and if there is no surviving spouse, the person in charge of the decedent's property must file and sign the return as “personal representative.
