i have created a player, nothing special about it. It works in all aspects exept for moving straight through invisible walls.

this is the c_move function i use:

See if making the walls thicker helps. This issue has me puzzled as well...

Wasn't there this "glorious" update that made things with the invisible flag also passable although the passable flag was not set?
I'm not sure about this, so check you DarkWhoppy's hint.
What you could also do is a simple trace instruction (with/without the flag ignore_passable set) to see if the invisible wall is passable or not.

Do you use poly-collision?
Have you set the bounding box (c_updatehull/c_setminmax)?
Is it passable also if INVISIBLE is off?
(I remember also such a behavior Xarthor mentioned)

Don`t make the wall invisible, set the Texture on each side to none

i tryed this but it is acting weird and the environment is lighted like there is a blok there even though it invisible. Also, when you make the wall a bit larger then the environment you can look through the space where the wall is.