Copying IOS

On January 6th, 2009 i instructed students how to copy IOS from router to TFTP server.
1. Run TFTP server on PC
2. Connect PC and Router
3. Give IP's to both device
4. Give commands on Router
Router(Config)# copy flash: tftp:
Asked for Destination File Name-------------------
Remote IP Address---------------------------------
Destination File Name-----------------------------
....................................................................................................................................................................................................
ERROR:But it was not working, the cable that was used between router and PC was Roll-Over Cable, although link was up.......................

so after 1-hour when i change the cable to straight over Cable and ping the IP it works and after that when i apply the copy command so it works.

Router(Config)# copy flash: tftp:
Asked for Destination File Name: ios-72600-17.3v
Remote IP Address: 200.100.50.1
Destination File Name: ios-7200-17.3v
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

If we use Roll over cable it will show that the link is up but communication will not be succesfull.