How to explain you were dismissed in an interview?

I was dismissed in May under Gross Mis Conduct for letting a parent into a contact centre, however I was told that the parent wasnt allowed into the building and the person who was advised of this said she had told me? I havent done anything about this as I am hoping to get a job without taking it any further as I have been under a lot of stress with it. I would like to know if any one could help me in what to say when I go for my interview in the same sector (care). This would be greatly appreciated.