Hello, I have a problem on my autocad 2011 mac. I m modeling and i have my 2d floor plan under my model, when i switch to conceptual view my floor plan lines extend. About 1 meter to one direction, if i switch back to 2D wireframe it looks normal. This happened to me before but not too sure how to solve it. Please help!

Extend in which direction?  Upwards?  If so then you probably assigned a value to the variable for THICKNESS which is normally set to "0".