Ok. Here's my command:
/tellraw @a {text:"HOVER OVER MEH",hoverEvent:[{action:"show_text",value:"Hi"}]}
and all I get from the commandblock is the stupid response: "An unknown error occured while attempting to preform this command" I have no idea if this is a Bug or not, but that's all I know.
You're doing it wrong. hoverEvent is no array.
Use this: