Comtrol ES7510-XT - Manual (Page 143)

RocketLinx ES7510-XT User Guide: 2000571 Rev. D VTY Configuration Locked (Error Message) - 143
Configuration Using the Command Line Interface (CLI)
VTY Configuration Locked (Error Message)
An alert message appears when multiple users are attempting to
configure the ES7510-XT. If the administrator is in Configuration
mode, then the web users cannot change settings. The ES7510-XT
allows only one administrator to configure the switch at a time.