Unable to set up Homesharing on AppleTV2

I had to reset my AppleTV2 and when trying to set up Homesharing again (to access media on my iMac) I am unable to do this.

It asks me for my username and password, however whilst i get the authorisation code on my phone, AppleTV simply tells me that my password is wrong and will not let me proceed.

Is there any way of changing this to allow me to log in?

Thanks