make sure you are in the directory containing ifcfg-wlan0. Be sure you are typing the file name correctly. Linux is case sensitive. Tab completion is a great tool if you don't already know about it. Just type part of the file and press tab. Works the same with directories and commands. This will complete the entry.
cp -v ./ifcfg-wlan0 /etc/sysconfig/network-scripts/
I have a feeling you might not be in the correct directory. Basically it's telling you the file doesn't exist in the location you're asking it to look.
If that doesn't work try the full path to the file
cp -v /home/user/directoryoffile/ifcfg-wlan0 /etc/sysconfig/network-scripts/