Header and footer undesired borders

Hi everyone,

I have a weird situation I cannot solve.

In one section of my document (and only in that section) I have a standard header and a footer composed by 3 cells, but the problem is that the border of every cell is displayed and I do not know how delete it.

The other problem, with is even worst is that I have 2 lines, same as those cell borders, that joints vertically header and footer.

I would really like to have back my nice white page without those annoying lines..

I attach a screenshot of an empty page of that section.

thanks everyone

Alberto