Help with gui Image property?

Basically I am wanting an image to be replaced with a different image when moused over, this is my code.

gui = script.Parent
gui.Image = "rbxassetid://154570980"

gui.MouseEnter:connect(function()
	gui.Image = "rbxassetid://154570976"
end)

gui.MouseLeave:connect(function()
	gui.Image = "rbxassetid://154570980"
end)

Output: 21:44:38.599 - Content failed because Input string was not in a correct format. 21:44:38.600 - Image failed to load: rbxassetid://15457_ovr.png: Request failed

An alternative I can think of is to have two images and make on visible when moused over and one not then vice versa.

Any help? What is the correct input for the "Image" property?