Tracks out of tune

I recorded several tracks with Cubase 5 with my guitar tuned with my tuner, bass and piano are keyboards. A few weeks later I wanted to add some more guitar, I tuned the guitar with the same tuner, but it is out of tune with the song. This is not the first time this has happened and I have no idea why. Any help would be greatly appreciated.

I figured out what caused my tracks to be out of tune. I changed the buffer size on my Audio Interface ASIO, when I changed it back to what it was the tracks where back in tune.