1. string replacement (or in first case - swap the string along its length - seriously, it can work!)
2. action may be a little high at the nut or bridge (be careful if you are messing with those areas though, but I do it all the time and SO LONG AS YOU ARE CAREFUL!) - basically - string theory and tuning assumes string is parallel to the fretboard. If nut or bridge are high, the string is actually acting as the long edge (hypotenuse) of a triangle - and that will throw tuning off.
3. If those dont work - you may have a mis placed bridge or nut slot - and things start getting tricky there
What uke to you have - this will help tell us whether it is unusual or not, and whether spending money on a fix is worth it or not