Default [Q] Flash Stock Rom/Change SKU without Root

Hey Guys,
I would like to change my SKU. I've found this thread and used the method mentioned there, but it doesn't work for me. I got a VF SKU and would like to change to WW on my TF300TG.

At the moment i've got Android 4.1.1, so I downloaded WW_epad-10_6_2_8-UpdateLauncher from asus.com. I know it's not the latest firmware, but I would like to try the OTA update after flashing the firmware. (just to see whether it works or whether the Firmware Updates are Mac-bound)
So I downloaded the file, unzipped WW_epad-user-10.6.2.8 and renamed it into EP101_SDUPDATE. Then I put it onto the root of my microSD and went into recovery mode, but there nothing happens. When I choose RCK, I only see that green Android thing with a red !. What did I wrong? Any suggestions?

Thanks for your help.
Best regards