TreeView with checkboxes draws red crosses

Hello, me and my colleague have encountered a problem with our treeview that contains nodes with checkboxes.

On any other computer than my colleagues, the treeview draws red crosses instead of checkboxes, like below:

The treeview itself works fine on every computer (if you press a red cross it acts like a checked checkbox), but we cannot find out why it draws checkboxes correctly on only his computer?

BR,

Lucas