solid difference between cylinders

hi folks!

i am trying to make a cylinder with holes, and for this i use smaller cylinders to make the mold.

is simple, but i have a problem and i cannot understand why is happening. two small cylinders somehow are not beeing used for the 'solid difference' component to create the holes like the others. they have all the same properties but with different orientation, could be this the problem?.

thanks,

J