EDIT: Turns out the solution to my problem is to use BindableEvents for server-to-server communication. I was super confused as to why this wasn't already a feature in ROBLOX - glad someone pointed me in the right direction.
I want to create a RemoteEvent that fires whenever a ClickDetector is clicked. However, my current code (which I adopted from http://wiki.roblox.com/index.php?title=RemoteFunction_and_RemoteEvent_Tutorial ) only works in Play Solo mode.
Whenever I test the code in a test server, clicking the button results in the following error:
FireServer can only be called from the client
None of the scripts I am using are Local scripts.
FilteringEnabled is NOT turned on - I am just using RemoteEvents for (what I thought was) the convenience.
Is this possible? Thanks in advanced.

2 comments
FireServer has to be used in a LocalScript.
https://www.youtube.com/watch?v=4Dc_bri9mjs&feature=gp-n-y&google_comment_id=z132jfgo5yusff2wn04cjtq4nundizeqbbg