Hi @FluffyMcDuckface, and welcome!
According to this page, the full error was probably something like:
Traceback (most recent call last): File “/usr/bin/fslint-gui”, line 27, in import gtk ImportError: No module named gtk
But there’s no way to be sure, and without more information, we’re shooting in the dark here. Please see [HowTo] Provide System Information, [HowTo] Post screenshots and links and [HowTo] Request support for more information and help to provide the required information.