I have been beating my head against the wall trying to figure this problem out. I have an object that is a portion of a hallway. Hopefully you can see from the image what its construction looks like. As a side note, the “Base” and “Ceiling” used to be one piece but I have broken the model (Blender model) apart (either way I get the same collision problem). This is also not a Blender file issue. I exported it as an obj and passed it on to a co-worker who uses XSI…same problem happens when he imports it into a scene as well.
The Problem:
In game, the player cannot pass through either end of the hallway piece because there is collision blocking the path. If the ceiling is completely flat this collision problem does not occur, but with the gutter and perpendicular beams, collision seems to be forming that will not let the player through. If I make the gutter and perpendicular beams into a separate object and place it in the world, the player will also get stuck. Does anyone have any idea why that is?
Update:
Maybe this is a Blender problem. My co-worker just modified my mesh a bit (that’s all it takes for the software to re-order verts and calculate normals) and no longer gets the weird collision problem when he imports it into his Unity scene. He sent me the modified object, I imported his new obj into Blender, saved it as a blend file, dragged it into the Unity scene, told it to generate colliders and it works as one would expect. Any Blender users out there that have had anything like this before and know of a solution?
Okay, I have figured out the problem. The problem isn’t Unity and it isn’t Blender…
As embarrassing as it is for me to admit this, maybe it will help someone else in the future…
my camera box is hitting the collision of the model ever so slightly…
So there it is…something so simple I never considered it. 
Upon further investigation it isn’t the camera box that is the problem…that camera clips through walls…it is the collision capsule/box around the player. So I have some new questions that might even warrant a new topic.
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Is there anyway in Unity to see the collision around the player when running the game?
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Is there anyway to prevent the camera from clipping through walls and reacting to geometry collision?