Before I got this error, Halo CE was running fine without any problem. When I took my laptop with me to work, Microsoft Controller check thingy has stopped working. NOTE I'm not playing Halo CE with any controller at all. XFire and Steam aren't connected online. After I came back home, I tried to run Halo CE again and got the error:

"Cannot allocate required memory. Some application has loaded where Halo needs to be located."

Are there any solutions to this problem?

Could be that you're running so many processes at the moment, that Halo just doesn't have enough memory available to run. Use task manager to check whether there is another haloce.exe or halo.exe running. If so, end those processes.

Googling the results didn't work so I found out, Xfire wasn't running which was also needed for this.

You might have to restart your pc.
I had it too once, restarting my pc fixed it.

To this point... don't you think he already did that?

Try this (just a troubleshooting):
- Clean your PC with Ccleaner. (Maybe a registry clean too while you're at it.)
- Turn it off.
- Turn it on.
- As soon as the desktop has finished loading, open up Halo.
- See if it still works.

I turned on Xfire which is connected and logged in and still works.