My W-2 tax return shows single under federal and married under State.?

My W-2 tax return shows single under federal and married under State.I went to personnel dept of my working place to correct them , cos last year i file married filling jointly.They said they can only correct it for the year 2007, and not 2006.What can I do if i want to correct it for year 2006( so that I can change the single to married filing jointly , husband working , wife not working)