CATIA VB.Net.edit axisSystem

I'm trying to reverse the zip direction of an axis system in CATIA, using VB.Net.

I tried the following :

Public Const catAxisSystemAxisOppositeDirection As MECMOD.CATAxisSystemAxisType = 2
`Public Const catAxisSystemAxisOppositeDirection As MECMOD.CATAxisSystemAxisType = 2

Dim axisSystems1 = selection1.Item(1).Value 
axisSystems1.Name = "Screw hole direction." & Num_hole 
axisSystems1.ZAxisDirection = catAxisSystemAxisOppositeDirection

With this it occurs an error. I tried the same in the VB6 editor inside Catia and it works. In VB.Net it doesn't.

I also tried to create a new axisSystem and I wasn't successful. I don't know what to do