So I'm green to Rooting. I purchased a used ATT HTC One X. It came rooted with Viper XL 4.0.0 installed. That ROM works fine, however, I would like to update/change it to another ROM. I installed ROM Manager and made a full backup of my current install. I tried using TWRP 126.96.36.199 to flash a new ROM. I did the Wipe and then tried to flash a new ROM. However, when the ROM install is happening (for any ROM tried) I get an error that says... unable to mount /system. Any help would be appreciated so I can get past this point and get another ROM installed successfully.