I left job A in Feb 2007. I already finished filing a return for this job in Feb. I switched jobs but I still received a W2 from job A as income earned in 2007. Could this be a error on their part?Should I just ignore it?

No it is nor error on their part.
You must report this income on your 2007 tax return. Now you need to file amended tax return.

How did you come with the figures to file for that job? Did you use your last pay check stub? Do the figures match exactly on your pay check stub and the w-2 that they sent you in 2007. Then what is the problem? You filed it as if you had a w-2. As long as the figures match, and you claimed the income, you should be okay. The IRS might ask you to send in your copy of the w-2 if you mailed in your return. UNLESS> You are trying to tell us that you actually worked this job in 2006 and claimed it on your 2006 return. Then mukata is right, you need to amend your 2006 and your 2007 if you're already filed.