it is border edge, which u can not delete. wht u have to do is move it to the closer loop/segment and merge the vertices with other segments' vertices and then again extrude it to desired length. now u'll be able to delete it. the basic concept is to merge the border edge to another edge
projects of my company
3D
https://www.youtube.com/watch?v=uPTmThoCrIY&feature=related - project - disney diwali (india based company)
https://www.youtube.com/watch?v=JSAfzqMBHqs&feature=related - project - 2 medhak (Public Service Ad)
https://www.youtube.com/watch?v=lMLR2L-swZo - project - ace bank commercial
https://www.youtube.com/watch?v=ZogNsf8k-xU - project - company Profile
2D
https://www.youtube.com/watch?v=82xV3bII9bU - project - (a fren named jimmy)