@dharttttttThe post by @abctax55 has covered the most logical explanations.  I would paper file the return with a cover letter to the IRS explaining it was rejected for e-file due to the SS# snafu. 

If identity theft is confirmed by the IRS your client will be eligible for an Identity Protection Number [PIN] for use in e-filing future returns.  The IRS will mail the IP PIN to your client each December for use in filing the current year return.  You can read about it here:  https://www.irs.gov/identity-theft-fraud-scams/get-an-identity-protection-pin