I had problems using, so I exported licience and remove application and re installed Acad LT now I can't get the licience to import back. I have the selection under acad lt 2007 but nothing happens when i click on it, nothing launches
You probably should not have done that... .
Windows version?
Autodesk recommended uninstall/reinstall procedures are as follows
Uninstall: http://usa.autodesk.com/getdoc/id=TS45252
Reinstall (for XP/Vista users): http://usa.autodesk.com/getdoc/id=TS75218
Ensure the user installing/uninstalling and using the product have enough rights to do so (install and reinstall as local administrator):
Unable to run AutoCAD® as a restricted user http://usa.autodesk.com/getdoc/id=TS1055299
More complete .NET fix if you did not go through this procedure:
http://forums.autodesk.com/t5/Installation-Licensing/NET-Framework-Cleanup-Tool-for-Unhandled-Except...