have a look in account setting on the tools menu? is there a duplicate but perhaps non functional account there?

I am trying to add an account by clicking Account Actions/Add Mail Account on the account settings menu. I enter the name, email address and password and click Continue. It does its little setup dance and lights up the Done button. When I click Done, I get a popup labelled Error Creating Account that says "Incoming Server Already Exists"

My question is, why can't I have two accounts, or seventy-seven accounts for that matter, on the same server if they all have different names? It looks a lot like a bug to me.