Why is this happening?

In a script I'm working on, I have a line of code that fires after it confirms a value inside a Frame exists. Here's the line of code:

repeat wait() until script.Parent.Value
	-- code here

The problem, though, is that even when it checks if it's not nil, the script breaks. The output reads:

:1:Value is not a valid member of Frame

Also, putting something like:

local value = script.Parent:findFirstChild("Value")
repeat wait() until value

just puts the script in an infinite loop, even if the value isn't nil. Can somebody please explain why the script is breaking?

Your loop doesn't change the variable value, so if value was nil at the beginning, it will always be loop forever after.

repeat
	wait()
until script.Parent:FindFirstChild("Value")

Conveniently, ROBLOX provides a :WaitForChild method that acts like :FindFirstChild except that it will pause until there actually is such an object, hence

thevalue = script.Parent:WaitForChild("Value")

should suffice.