Firmware upgrade encountered error when going into Recovery Mode My Galaxy GT-N8000 is showing this message Firmware upgrade encountered an issue. Please select recovery mode in Kies and try again. I cannot enter into recovery mode. It keeps showing the same message. What can I fix this?
It's a known issue on Samsung phones. When an update is interrupted or fails for whatever reason, the phone will not boot in either normal or recovery mode, and will present the "Firmware upgrade encountered an issue..." error.

The solution is to start the phone in Download mode (usually by holding the Volume Down button while powering it on from turned off state,) and then try re-flashing the update.  If you are having trouble with Samsung's Kies software, you may want to try Odin or Heimdall utilities.

It's not necessary to flash the full ROM to get rid of the error, you can flash a modem firmware of a custom/stock Recovery instead. Just make sure whatever you are planning to flash is designed for your specific device model.  As long as the last flashing attempt completes successfully, your phone should no longer show the above error, and allow you to proceed with voiding your warranty ;)