cannot add additional accounts in mac mail

I need to set up an additional account in my email. Using OS 10.7.2. I have done this successfully before but now I get "check username and password" on the first step. Since this is a new user, the message doesn't make sense. It's not letting me create an additional user account no matter what I do. I'm suspecting software coruption and would reinstall but the system came on the HD and I do not have install discs. Can't afford to buy system upgrade and risk having to upgrade alot of other software as well. Can I fix this problem?