Yes, I got this red x and I upgraded to 4.2 and it stayed there.
I could remove it by shutting down DXO, go to explore and move the folder elsewhere, start DXO without the folder and exit again, mopve the folder back and now I can ready it (and it asked also to install Z24-200 RAW & JPG module) and red x is gone.
Sorry, a normal refresh (which is offered ion menue on folders) should actually correct such cases or?