snapping problem in Photoshop

Hi, i'm working on a website layout for my work, but i keep running in to the same problem... i need to slice the buttons so that every button becomes a different image, but my slicing tool doesn't snap to my guides as it is supposed to...
anybody know the solution to this! even my boss doesn't know how come... (and yes, i do have "snap" and "snap to">"guides" turned on)

thanks!