Uninstall GUI mod and then the Widescreen mod in the Tutu directory and install them in the reverse order. Or if you don't have a GUI mod or the Widescreen mod in the Tutu folder, then you need to uninstall the Tutu, and then uninstall the Widescreen mod from the BG2 game and then reinstall the Tutu, as it needs to be a vanilla BG2 game... and then install the Widescreen mods to both game directories after the conversion is done.
Yes, this is about the fact that the Tutu Conversion is meant to use the vanilla BG2's GUI as a resource, and if it's modified by a GUI mod or the Widescreen mod before it's supposed, it gives those blank black spaces in the wrong spots in the Tutu interface and you see the translucent blacks that store the images on top of them, which is why the cursor trails are permanent. And here's a
post I made about it a long time ago.