Trouble after adding several tracks

Recording

I am having trouble once I have added 7 or 8 tracks. The following track added will be a couple seconds off the beat. Nor sure why. Is it a wave-lfile situation? I have to mix a song down after 8 tracks or the song gets out of whack. Any ideas?

Thanks.

What are your systems specs and what soundcard and drivers are you using?

You may need to increase your buffers??