Hello MayorCrispy, if you have exceeded the maximum number of computers One Care should generate this message:
"Unable to verify account status because the maximum number of computers is already activated for this account".
If your error message says "incorrect password" it usually means you have entered an incorrect password. To verify you are using the correct password sign in to your One Care account at billing - https://billing.microsoft.com/home.aspx
If your password is correct and you continue to get the incorrect password when attempting to activate, please contact support. How to reach support - http://forums.microsoft.com/WindowsOneCare/ShowPost.aspx?PostID=2421771&SiteID=2