Sadly that was what we tried, a fresh download and a new FSUIPC install as well.
No effect of neither, we still had the christmas tree effect.
We also tried a few different versions of FSUIPC including the 4.60a that I use and stick with for my another company 747.

Only thing we didn't try was a reinstall of FSX, he has some other addons and it was a pain tweaking the FSX install (FPS issues and crashes) to make it run smoothly and naturally he doesn't want to repeat that.
Anyways, I told him his next step is to ask Captain Sim themselves for help on this, I have gone as far as I can with it in that regard.
A little sad really, could have been considering the 757 pending its  price and cargo capacity in Air Hauler if I started a new company (Got my 747 right now.)