Thanks to @Global on the Gmod forum here on steam for this alternate method that works far better.
It admittedly does not 100% remove the LUA errors as they do still pop up for around 1/100th of a second but they are nearly impossible to notice.

For more detail here is the link to the discussion. https://steamproxy.net/app/4000/discussions/1/616187839439998169/

Originally posted by Global:

This is somewhat easy, however if you mess up you might need a reinstallation.
Goto your Garry's Mod installation folder (normally Program Files (x86)/Steam/SteamApps/common/garrysmod/garrysmod/), and go into the lua folder, then go into the menu folder. There will be a errors.lua file, open it using wordpad. Look for the following value:

local EndTime = SysTime() - 10

Change that 10 to 0 to completely disable it, or 1 to at least know when there's an error. Then save it, after backing up the file. See, if there's a lua error in one of the menu lua files, the game won't launch. If it breaks and you can't seem to fix it, validate cache.

If that does not work try this

Originally posted by GodPhase777 (mattbi777) :

When I changed local EndTime = SysTime() to 0 I still saw the errors popping up and glitching, however I did find a fix. Your gonna want to copy your original errors.lua and put it on your desktop somewhere safe so you can switch back to seeing errors if you need to.

After you've done that, go into the original errors.lua which is in your gmod folder, and simply set every number you see to 0. this should make it virtually impossible for the game to display an error as the error box is so small that its not even there.

subscribe to this mod and make shure that it is activated.

that's it.

Now you should have no error models showing up in your game (if there is a missing model it will be invisible.)

Note that this does not work for everyone (many people have this not work or only work partally).

there are two methods of removing the lua errors that pop up on the top-left corner of your screen.

(1) remove all mods that are causing errors even though your game works fine anyway.

(2) use this[www.facepunch.com].

now I will tell you how to install it.

step 1. download the file.
step 2. create a txt document wherever you want.
step 3. rename the txt document from insert the name you picked here.txt to insert the name you picked here.lua.
step 4. paste this into the lua file (use your favorite text editor for this)
require("luaerror")

lua_showerrors = CreateConVar("lua_showerrors", 1)

hook.Add("LuaError", "LE", function(err) --Return anything other than nil to stop the standard error display
local var = lua_showerrors:GetInt()

if (var == 0) then
return false
elseif (var == 1) then
Msg(err)

return false
end
end )
step 5. move the lua document you created in steps 2 through 4 into C:\Program Files (x86)\Steam\SteamApps\common\GarrysMod\garrysmod\lua\autorun\client (on a windows system)
step 6. take the dll file you downloaded and put it in C:\Program Files (x86)\Steam\SteamApps\common\GarrysMod\garrysmod\lua\includes

and then you should have no lua errors pop up at the top-left corner of your screen.