It looks like it was my lucky month !!!
To allow users to choose multiple filters on a table, i put a grid on a form.
clicking on a command button i minimize it to the headerheight value

.mygrid.height = .mygrid.headerheight + 1

clicking on its header i maximize it

.height = heightval

It works fine, or better it works perfectly on all PC but one.
On this bloody one it gives me the error that the object miagrid has evaluated an illegal value. This doesn't make sense to me.

Alessio

PS Thank you all once again