setValue in GXT ComboBox

[U]

Hi!
I want to change the Value of a GXT ComboBox with the ".setValue"-Command.

The Combobox looks like this:

.ComboBox

-> Entry1
-> Entry2

Entry1 is selected automatically.

So if I want to select Entry2 with the ".setValue"-Command (.setValue('.ComboBox','Entry2')) the Value won't change.
It's still Entry1, who is selected.

Is anyone out there, who knows how to fix this problem?