I have just installed mountain lion and I now have a issue with outlook I have a box with select an identtity coming up what should iI do

I have just installed Mountain lion and I now have an issue with outlook which I had to re install to access my excel files that would not open after the upgrade,however outlook is my challenge now. I have a box coming up with select identity coming up and anything I do does not resolve it it just comes up with an error occurred while launching. What should I do to resolve this ?