Background floor trouble

When i am walking in my environment, the character goes through the floor and the floor doenst become solid anymore. It then disappears while im walking. How can i permanently fix this?

It sounds like a physics problem… Perhaps a blend file?

Check the collision detection bounding object.

I’ve had problems with the ‘Convex Hull’ in the past. Most of the time I just use a bounding sphere.

“Normals” problem, maybe?!
Select all verts and do “Ctrl-N” to recalculate!