Simple. The object you are attempting to modify has been painted. Remove the painting (some or all) from the area you are trying to modify. Then your modifier will work.
I had the same problem as dfuytn and I figure out a way to counter it.
- Create a cube and a modifier.
- Change the setting of the modifier for your need.
- Copy-paste (ctrl-c ctrl-v, otherwise their is no way to copy paste it) the modifier into the object you want to modify. Make sure you select your object while you past it so the modifier apply.
Same problem here and it did the trick!
Many thanks
I would add that if changes need to be made to the modifier, they must be done in the same way: on the cube and then copy and paste again.