I want to know why, during an AutoCAD session, When I click within any command, it crashes and appears in command line "copyclip - select object", and the cursor(arrow) change to a selection square?

When did the problem first occur?Is it only happening in one particular drawing or any drawing you work in?What version of AutoCAD are you using?  Is it current with any/all service packs or updates?Was the drawing that you had the problem with originally created using AutoCAD 2007?

use autocad 2010 or higher to avoid this problem

[QUOTE=webgain]use autocad 2010 or higher to avoid this problem [/QUOTE]
Since the OP did not state what version he is using how do we know it isn't 2010 or higher?
If the version he is using is older than 2010 he may not have the option to change to another version.  Maybe it's a money thing.
How can we help him with the problem he has now?