check the w-2 is that your correct SSN? is it the correct year? if it is the problem may be that the employer never submitted w-2's to the SSA which forwards w-2 info to the IRS. as suggested, I would try calling the IRS first but if you can't get through send a copy not the original to the IRS with its notice and an explanation that you're enclosing a w-2 received from your employer that apparently is not on file.
