Comtrol ES9528-XT User Guide - Manual (Page 138)

138 - VTY Configuration Locked (Error Message) RocketLinx ES9528 and ES9528-XT User Guide: 2000508 Rev. G
Configuration Using the Command Line Interface (CLI)
VTY Configuration Locked (Error Message)
An alert message (VTY configuration is locked by another VTY)
appears when multiple users are attempting to configure the
ES9528. If the administrator is in Configuration mode, then the
web users cannot change settings. The ES9528 allows only one
administrator to configure the switch at a time.