After programming a device in Xpress Configurator, after changing the device's PID, an error message may appear stating:
Cannot determine if device has re-enumerated after reset!
It is likely that a driver associated with this VID/PID combination has not been installed on this machine. If it has, it's likely that there are multiple VCP drivers installed on the machine, the older of which is still being used by Simplicity Studio.
Use the USB Driver Customization software (AN220, located here: http://www.silabs.com/support/resources.ct-application-notes.ct-example-code.p-interface) to create a new driver with the custom VID/PID combination that you have programmed to the device.
If the device still fails to enumerate after installing this driver, make sure to uninstall any previous drivers on your machine. In Windows, this can be accomplished through [Control Panel] > [Programs] > [Programs and Features]. From here, sort all installed programs by "Publisher", and uninstall any "Silicon Labs" or "Silicon Laboratories, Inc" programs with the Name of "Windows Driver Package - Silicon Labs (silabser) Ports ..." or "Windows Driver Package - Silicon Labs (silabserenum) Ports ...". Then re-install your customized drivers.