If you're filing separately, you can claim an exemption for your spouse if s/he had no income, isn't filing his or her own return, and isn't a dependent on someone else's return. However, that is not the same as claiming that perosn as a dependent.
Head of Household filing status requires a qualifying dependent, such as a child. Did you have one listed on your Federal return?
But you could have avoided all this by simply filing Married Joint. So why didn't you?
