Scoreboard and testfor issues using commandblocks

I'm building on a map in Minecraft, where a player (myself for example) will press a button and his status changes into "The Player is ready for the game to begin". So, press button -> /scoreboard players set @p IsReady 1

Now I want to test if the player is ready, so

Redstone clock -> /testfor Untertreiberman[score_IsReady=1]

The command block tells me that it can't find the player, but I'm there with a status of "IsReady 1".

When you use a /testfor command, you can't use specific usernames to test for people on the server/world.

When testing for people with your score IsReady, use:

/testfor <selector(@p)>[score_IsReady=1]

So when someone is near by the commandblock, it will return true only if someone has IsReady=1.