Outlook Contacts

I’m running Outlook 2007 on Windows 7 Pro. I have a problem with Outlook changing email address associated with a contact. I’ve tried to delete the contact and readd it but still having the same problem.

Example: Joe Smith jsmith@123.com is what I have been using for months. All of a sudden when I type in Joe smith it shows his address but when I send it goes to someone else at a different company, ie. ssomething@abc.com.

Does anyone have an idea what could be the problem? If I open the contact and try to delete his email and reenter it it will change to the address it is sending it to (ssomething@abc.com).

Thanks