Aha! <kuid2:101046:100236:35> Right-Hand Drive DES - This is the only faulty asset shown in my Content Manager list due to the following errant components by Author arraial:
<kuid2:524343:6639:1> car 28 UK - Van_ford_e250s
<kuid2:524343:6642:1> Car 31 -Jp- car mazda rx8
<kuid2:524343:6643:1> Car 32 - Jp- Car Mitsubishi Magna
I installed your Right-Hand Drive DES region recently following discussions in another thread about Region issues and found that it didn't work for me either, presumably because of these problem carz.
Found that I could not pick it up in the Route Edit... Region settings dialog combo box.
If you were to fix these assets (missing nightview.im mesh) or remove them from the assets table in your config.txt, then the region should be selectable and work properly again.