It means that your federal tax was withheld at a rate lower that 6.2% (which is what Social Security is withheld at).
Your federal tax was withheld at a rate of 4.54%.
It probably isn't an error: depending on how frequently you were paid and how big your paychecks were, the withholding was probably calculated correctly.
Employers use Circular E to figure out how much to take out of each check for federal based on your filing status, which is why you filled out a W-4.
