all commands must be in fastboot. USB debugging must be enabled..
you can use the command fastboot reboot recovery anytime, it doesnt have to be after flash, it just has to be whilst your in fastboot.
otherwise use 'adb reboot recovery'
C:\android>adb reboot recovery
adb server is out of date. killing...
* daemon started successfully *
error: device not found
mmm .. there is a problem ...