I've started making sketchup models not long ago and I'm still learning to use the program. Whenever I make a door or window there will be invisible collision blocking the way and you cannot pass through. There is nothing there in sketchup and ingame you don't see anything but you can't go through it. Why does this happen and what am I doing wrong?

Rather than just cutting a hole through the model, I would recommend planning how big you want the hole, and constructing the wall around the space.

or try making a .option file for your msh with -donotmergecollision as it's contents

Woah, that worked Fragme thanks a lot.