That doesn't sound too good. I'm assuming you're typing in the right password? If so then you might want want to notify them of your problem and once you get back in to your account change your password out.
Betfair Customer Services 18 Oct 11 08:50
We are aware that some customers are having log in issues with Betfair at present. Please be assured that our engineers are working to resolve this issue as soon as possible and we hope to resume normal service shortly.
We will update this page with any further information as and when it is available.
I figured you were typing it correctly sir. Just make sure to change out your password to be on the same side once you get back into your account, especially after seeing what has happen to others who've played there over the course of the last 18 months or so.