Put something straight along the fretboard, if one fret is higher that the rest then this one will need filing down (in small increments so not to go to low) and then reprofiled and polished. If one fret is lower than the rest then this will need replacing with a higher one.
Could also be caused by worn strings, a warped neck or the truss rod may need adjusting. Take it somewhere to get it checked out then fix yourself or you could make it worse as could be multiple causes
Greg, February 2007
