Since the last update i get this error. I already re-downloaded the plugin but it still happens. My other 20 plugins work just fine.

Error while compiling: PlayerAdministration.cs(923,25): error CS1061: Type `BasePlayer' does not contain a definition for `EnableServerFall' and no extension method `EnableServerFall' of type `BasePlayer' could be found. Are you missing an assembly reference?

There is no reference to EnableServerFall in PlayerAdministration. Please verify that you are using 1.6.7 downloaded from the only valid sources:
https://umod.org/plugins/player-administration
or the GitHub linked on that page.