@charlieboy999, i had a similar situation. At the same time, I did not see the certificate in the list of user certificates.Sorry, I didn't read the guide properly and realised that the pack you sent needed VB. Managed to get up to setting the proxy on the tablet. Unfortunately, I don't think that the certificate installs properly as others have said. I still can't access asus.com for example. I'm able to go to mitm.it and download the certificate (it doesn't even ask for the pin that I set and just asks me to name the file) and I get "*proxy name chosen* is installed" but the unlocker still shows the same error as before, sadly.
Make a system certificate in Ubuntu according to this instruction and copy it to /system/etc/security/cacerts/
Reboot your tablet and try again.