[HardRock]

ppppppppppppppppppppppppp

[Sandiel]

1. You made a global variable named "string" (on top of your script)
2. You made one or more local variables named "string" in different/one callback(s)
3. The variable shadows a variable at a preceding level.

Fix:
Rename either the global variable or the local variables (plural, multiple variables) and it will be fine.
Hope this helps, the easy and fast way would be to rename the global variable rather than renaming the other local ones, good luck.

[HardRock]

Dont understand