The Tubuntu installer application will not install the updated kernels for SBK1 devices and the manual procedure in post #2 will tell you what you need to do.
OP for Tubutnu by x3maniac
1. Download the newest “tubuntu v0.x.x” without Prime (system.img) or Ubuntu.img as it is written in the OP.
a. This download contains the application, boot.img file, and basic kernels available at the time of this guide needed for installation. There will be updates for kernels specific to an Ubuntu image as the developer is able to work on them. Check for new downloads and posts.2. Extract all the files in “tubuntu v0.x.x” to a Tubuntu folder wherever you wish. 7-Zip is the zip program of choice but any others should work fine.
b. The download also contains drivers and installation for APX mode located using the “Other” tab in the application.
c. This download does NOT contain the Linux operating system nor the Android ROM.
3. Download Prime ROM [stock hc w/ root](system.img)
a. This download is the system.img that contains a root enabled Android ROM.4. Extract the system.img file from this download.
a. Copy this file to the \images directory. The images directory is a sub folder of the TF-101 Ubuntu Installer application that you extracted in step 2.5. Download the Ubuntu image of your choice.
a. Currently there are 2 Lubuntu downloads. Read the bullets and determine which one you want.6. Extract the image file of this download and place it in the \images directory. Rename this file to ubuntu.img.
7. Open the TF-101 Ubuntu Installer application.
8. Connect your usb cable to the TF-101 and the computer.
a. Shut down the tablet.9. Enter APX mode by holding the volume up button first, then hold the power button until you hear the usb sound from the computer.
a. Your screen will be black and the TF-101 Ubuntu Installer application will light up green and say APX Detected if you correctly entered APX mode.10. Change the dropdown to SBK 1 located directly below the green APX Detected text.
11. Click on the Flash tab.
a. Select Android/Ubuntu and then hit Flash.12. You will see an install log in the right of the application. Mine takes about 15 minutes or so but you will know you are finished when you see the Android ROM load as well as the red text APX NOT Detected (in case your screen is off when you come back).
b. Android is the primary boot option here.
13. Proceed with setting up Android. DO NOT reboot or power off before the initial Android set up is complete.
14. Once completed and you wish to enter Lubuntu, power off the TF-101 and hold down volume down first and then power. You will see your screen say hit volume up in 5 seconds for recovery. Hit volume up within 5 seconds and it should boot your Linux graphical desktop environment.