Having problem adding iphone app in App store

Hi!

I made my first Iphone app and now im having problem with adding it in App store. I succeeded adding app information in Itunes Connect but when im validating that app in xcode it says "The private key for "company name" is not installed on this Mac". I have reinstalled almost everything in Apple developer and it still says that.

I made this application with my older Macbook then sent it in this Macbook. Can that make some errors?

My older Macbook has xcode 4.2 , Macbook 10.5.8.

Thx!