✓ Accepted answer
One of the URLs you have is what it mentioned http://www.roblox.com/asset/?id=614196198,rbxassetid://614212267. See, that's one string, not two -- the comma is a character in the URL.
You should presumably split that string up into two strings.
My I suggest formatting your table on multiple lines? Unless they're very small, it's usually best to put one thing per line:
GIF = {
"rbxassetid://614166207",
"http://www.roblox.com/asset/?id=614196198,rbxassetid://614212267",
"rbxassetid://614243948",
"rbxassetid://614245502",
"rbxassetid://614624256",
"rbxassetid://614652355",
"rbxassetid://614749146",
"rbxassetid://614750178",
"http://www.roblox.com/asset/?id=166249907",
"rbxassetid://614751359",
"rbxassetid://614755688",
"rbxassetid://614756818",
"http://www.roblox.com/asset/?id=166249942",
"http://www.roblox.com/asset/?id=166249964",
"rbxassetid://614758943",
"rbxassetid://614761035",
"rbxassetid://614764045",
"http://www.roblox.com/asset/?id=166250031",
}
It makes large tables easier to manage, and especially highlights inconsistencies