According to Fannie Mae and Freddie Mac rules, your credit rating, as you described it, should not be a barrier to a HARP refinance http://www.bills.com/harp-mortgage/. However, lenders can apply stricter rules, called "overlays," than Fannie or Freddie require.
Your ability to refinance is also affected by:
1. Your LTV- some lenders are restricting HARP refinances to 125% LTV (loan-to-value) or less. Others won't take loans with over 150% LTV.
2. Your property type- If you have a condo, it can be more difficult to do a HARP refi than if you own a home.
3.Your DTI- A lender will check your debt-to-income ratio.
Your best step is to shop around for a HARP mortgage. If one lender turns you down, keep looking, because different lenders are applying different standards. Also, if you get turned down, make sure to find out the specific reason you were denied.