Mine did the same. Restore to Default as in the suggested answer did not work for me. Here's how I fixed it. Edit>Toolbar. Scroll down to the paint bucket that for me was showing up as if it WAS on my toolbar even though it wasn't. What WAS showing up on my toolbar was the 3D paintbucket and the other tools under it were missing (the gradient and the paint bucket). So, I just dragged that 3D paint bucket over to the right side of the column so it wasn't selected to show in my toolbar. Clicked Done. Now my paint bucket and gradient are showing up again.