Because my post at bug reports wasn't getting much... sorry... ANY attention, so I posted it here.
Ok, this is by far the most stupid error I have ever had...
So I made a level with all kinds of stuff, and it worked fine. I did an extra hallway with all the same stuff, nothing new and it started erroring in saving textures in test game. And now I deleted that hallway and the level is same it was when it worked fine and it still errors at saving textures. This is really pissing me off, because I don't really know what texture is the one that is problem here. And it wasn't a problem some time ago. So that is even weirder.
To be more simple:
I made a 2x2 box room with FPSC and put a wheelchair in there. I made another box with a wheelchair in there, that is EXACTLY the same textures and everything, but it gives me the usual runtime error. Now I delete the other 2x2 room and the wheelchair in it and I have the same room that I had in the beginning, that worked fine. But now it errors on saving textures, even thou nothing is changed.
(I didn't really make 2 box rooms, that was just a way to make things clear that you all understand my problem. )
Other thing would be nice, if it told me what texture it is, that is not working, like I can see what entity is for some reason wrong, if it bugs there, because it says what entity it is "building" there.
But thanks everyone for replying and helping me with my bug!