It often happens that there are problems efiling the year you switch from an ITIN to an SSN. It's not so much a problem of the software, but a problem of the efiling database of the IRS (mainly when they update the data).
If entering Zero doesn't work, you should file on paper.
You should also inform the IRS of the switch to the SSN so they can combine the tax files.
http://www.irs.gov/Individuals/Additional-ITIN-Information
What do I do when I am assigned a social security number (SSN)?
Once you receive a SSN, you must use that number for tax
purposes and discontinue using your ITIN. It is improper to use both
the ITIN and the SSN assigned to the same person to file tax returns.
It is your responsibility to notify the IRS so we can combine all of
your tax records under one identification number. If you do not notify
the IRS when you are assigned a SSN, you may not receive credit for all
wages paid and taxes withheld which could reduce the amount of any
refund due. You can visit a local IRS office or write a letter
explaining that you have now been assigned a SSN and want your tax
records combined. Include your complete name, mailing address, and ITIN
along with a copy of your social security card and a copy of the CP
565, Notice of ITIN Assignment, if available. The IRS will void the
ITIN and associate all prior tax information filed under the ITIN with
the SSN. Send your letter to:
Internal Revenue Service
Austin, TX 73301-0057
