Minecraft Realms crashes whenever I try to log on my alts realm

Put the summary of the bug you're having here

What I expected to happen was...:
I expected to log into the realm and finish my build.

What actually happened was...:
I was on for 1 second then Minecraft crashed.

Steps to Reproduce:
1. I was reading an article on how to give yourself a custom head (http://www.planetminecraft.com/blog/how-to-get-a-custom-user-heads/),
2. I saw this comment,
hey, i have this:

/give @p skull 1 3 {display:{Name:"bird"},SkullOwner:{Id:F32F440A-A44E-1286-64EE-2C9E9BEDD2C5,Properties:{textures:[{Value:e3RleHR1cmVzOntTS0lOOnt1cmw6IjNkLnBuZyJ9fX0==}]}}} 

but i cant use command blocks, i just need the usernames, but idk the username for this. i did a command generator and got this, know how i can find out the username for this head?

3. I put it into the command block and now I cant log back on, Please help!