Your browser does not seem to support JavaScript. As a result, your viewing experience will be diminished, and you have been placed in read-only mode.
Please download a browser that supports JavaScript, or enable it if it's disabled (i.e. NoScript).
Assuming you aren't doing this on Origins, it's currently bugged and we are working on it.
Please take a look at this topic from JezuzLizard - he created a workaround for this! https://forum.plutonium.pw/topic/308/release-zombies-map-restart-clientside-issues-workaround/