Flashing CM 10.2 to 11 TWRP flash not working
You can install it,

First of all try to update to a new TWRP version if possible like you installed it before.
Or you might want to go to the bootloader/fastboot on Samsung devices you need to press 

Volume up + home + power 


On other devices you must press

Volume up + power


and connect your phone to your PC and install the drivers if not done before, you can install the naked Adb drivers from twrp's site.

This is the link for your device:
https://twrp.me/devices/htconexplusinternational.html

You also can connect it to your PC install the drivers and type

adb reboot bootloader


You can find more info on TWRP's site.

put the Gapps/Google apps on the SD card, you might want to use 

adb shell push gapps.zip /storage/sdcard0/
Downloads


All after each other.

Or setup mtp for TWRP.

You can do this at the settings mount and enable MTP.

Then push the update zip to your device which is the same as above.

Install the update and wipe the caches.

Then you're all set.