[Asus  Eee Pad Transformer Prime] mattnmag:
It sounds like you have successfully generated the wheelie blobs. The error message you're getting just means that they didn't get uploaded to the AndroidRoot webserver as an additional backup... but they should still be created in a file folder called AndroidRoot on your tablet's /data/media partition. Use a file explorer app like ES File Explorer and look for them in the AndroidRoot folder. You could use adb commands to pull the files over to your computer... or you can also connect your tablet to the computer via usb cable and easily copy the wheelie blobs to your computer for safekeeping. That's what I did, and then I backed them up onto Dropbox as well to have a duplicate backup.

If you haven't found this guide already ( https://matthill.eu/android/transformer-prime-tf201-jellybean-nvflash/ )... then check it out because it helped me tremendously with the entire NVFlash process. You should be good to continue following the guide to complete the entire NVFlash backup process.

As far as flashing a custom recovery to the device, I chose to flash TWRP and used fastboot commands to do it. If you are new with fastboot commands, then there are some good general guides that you could find through a Google search that would be helpful to read for general knowledge purposes. Here's a good General fastboot guide for reference .

The fastboot command to flash a custom recovery for the TF201 is ( fastboot -i 0x0b05 flash recovery “and enter the name of desired recovery file here”). I chose to download the official TWRP blob ( twrp-2.6.3.0-tf201-JB.blob ) from TeamWin’s TWRP website at https://dl.twrp.me/tf201/ and then flash that to my TF201.

Here's the steps used:

(**YOU MUST HAVE AN UNLOCKED BOOTLOADER TO DO THESE STEPS *** please use them at your own risk and only if you feel comfortable with what you are doing-- you could brick the tablet if you do something wrong).

1. Copy the correct TWRP Recovery blob into the same folder on your computer as where you have fastboot.exe (for me, this is in my Android SDK platform-tools folder). Then hold Shift on the keyboard and right mouse click on any open white space in the file folder, and open a command prompt terminal by clicking "Open Command Window here"

2. Boot into Fastboot mode on the tablet with volume down/ power, then navigate to usb icon and press Volume up to enter fastboot mode. Plug the tablet into the computer with the USB cable. (Now, it would be a good idea to enter the fastboot command: " fastboot devices " without the quotes... and confirm that the phone is communicating with the computer by showing your device's ID number).

3. Enter this fastboot command: fastboot -i 0x0b05 flash recovery twrp-2.6.3.0-tf201-JB.blob

4. After giving it time to complete the process (at least several minutes) and getting a message in command terminal that it was successful, you will need to hold the power button down on the tablet for about 10 seconds to let it boot up normally. After it boots up, you should be able to power down, then hold Volume down plus Power button to boot up into recovery screen mode--- then volume up on RCK to get into TWRP recovery.

(I adopted instructions from flumpster's instructions in this thread and from instructions in this Guide ...so credit should go to them.