An item with the same key has already been added (Site Selec

Hi,

Whenever i try to edit the site selector widget I get the error " An item with the same key has already been added" . I have attached the log file which details the error. 

This error only occurs on one of our databases, so i know nothing is wrong with the solution code per say. 

I saw on another thread that installing and uninstalling the dashboard may fix it, but that is not an option. 

Thanks for your help.

Regards,

Zubair