File import error on Pro Tools

Hello,
This particular problem occurred after I imported a file in Pro Tools v.9.
It wasn’t any bigger than the ones I usually work with but since then every time I click play I get this error message:
A CPU overload error occurred. If this happens often, try increasing the “H/W Buffer Size” in the Playback Engine Dialog, or removing some plug-ins. (-6101)

I’m using Mac x snow leopard OS, and I’ve never encountered a problem like this one before.
If there’s any way you could help please leave a post.
Thank you in advance.
