Why am I receiving this message?
You are receiving this message because you are using Gredwitch's Base, and it has detected that you are currently using the 64 bits branch, which makes it unusable!

How do I hide this annoying message?
You CAN'T. You will either have to remove Gredwitch's Base or to switch to a non-64 bits branch.

The 64 bits branch is the only way for me to get enough FPS so that the game can be playable!
You probably didn't look too far to improve your FPS. First of all, you gotta know that the Source engine (what GMod uses) is a very CPU intensive engine, and Garry's Mod doesn't really have multicore support (the Multicore Rendering option in the video settings doesn't actually do anything). But you can still do some hacking to get way better FPS!

To do so, go in your Steam Library, right click on Garry's Mod, select Properties, select "Set Launch Options" and add these to it:

You should get a significant FPS boost from these options.

I don't care, the 64 bits branch is all I've got!
You can try to use it, but don't expect me to help you in any way if you have a problem. As some good forum says :

Originally posted by "some good forum":

* Your warranty is now void.
*
* I am not responsible for bricked devices, dead SD cards,
* thermonuclear war, or you getting fired because the alarm app failed. Please
* do some research if you have any concerns about features included in [THE 64 BITS BRANCH]
* before [USING] it! YOU are choosing to make these modifications, and if
* you point the finger at me for messing up your [GAME], I will laugh at you.