I think I can only help out with the syntax that works with what you're posting. I have no idea if it will work with your real database. First, as I think I noted, I don't use macros so I removed the embedded macro and used the AfterUpdate event of the control. You click on the ellipses (...) in the property sheet to get at that. Do that and enter the code lines between Private Sub and End Sub so that it looks like this:
Code:
Private Sub TBXricerca_AfterUpdate()
Me.Filter = "campo1 LIKE '*" & Forms![navigationform].sottomascheraspostamento.Form.TBXricerca & "*' "
Me.FilterOn = True
End Sub
I got the form to filter using that. If you put in a value that is not in the records, it will jump to a new record. Not sure if that's ok.