Why do my properties show up as '[string contents] not found' during debug? Im pretty new to the BGE and Im just getting to grip with Logic bricks

I recently attempted to create a property named Next (String) that holds the word Up, Down, Left or Right inside it depending on user inputs.

My problem is that Up is the default starting direction which seems fine; although as soon as I attempt to change it it becomes [Up/Left/Right/Down not found].



It seems like this problem is effecting other parts of logic that refer to the Next variable.
I guess I'm a little idiotic for not noticing but I've found my own answer and I guess I should leave it here for future reference!

When changing a strings data the word needed to be stored inside quotation marks (e.g -  "Up") or it won't work, hope this helps someone in the future.