Same issue here. I am running WP in Network (multi-site) mode; you too?
Also, did you find a similar plugin that works? I also tried WP Maintenace Mode and is not working either…
I uninstalled wp maintenance mode and installed maintenance mode. After activating it, in the settings, there is an additional setting: Activate/Deactivate Maintenance Mode – set this to ACTIVE and this one works.
I just downloaded it, activated it then went to settings and set the mode to active. Works perfectly.
I had the same problem with a new installation. I changed the theme from Twenty-Eleven to Twenty-Ten then it worked.
