I am using Autocad 2010. I have been using 2008, but recently upgraded. I have a project that one particular file is driving me nuts! I can not use trim or extend on any existing line work. However, if I draw two non intersecting/crossing lines and ust the 'TR' command it works fine. I have checked to see if all lines are in the same plane and the appear to be. The only way I can trim or extend is if I use the 'Flatten' command. Can anyone help with this issue?