Have you checked the system values on the AS400s? Maybe they all have QAUTOVRT setup with a number of devices or *NOMAX except the one you can’t connect to.
The fact that you can connect OK to most of them, except your one lucky machine, would suggest that the problem is with that machine, rather than your emulator software or Vista.
Also check the <b>device name setting (Workstation ID)</b> under the communications and configure.
If the specify workstation is populated you must verify that the device name isn’t already in use on the AS400.
If so blank the field or assign a new value and try again.