"I lied when I said I was a liar"

Now, look at the above statement.  For the two events described above, there's a few possible things:

• You lied in both occasions
  
• You told the truth in both occasions
  
• You lied once, and told the truth once

If that's so, which did you do?  (if you said you lied once, and told the truth once, say which one you lied to and which one you told the truth about)