A number of possible reasons.
It may in fact not be a true dng file and QU recognises that from information embedded in the file because the conversion process by LR has not truly created a raw file:
Right click over the thumb and select Display Image Info (near the bottom of the drop down list) and see what it says - is it 48bit or still 24 bit from the jpeg? See screen shot below.
QU may not be set to use raw files in File/Settings/Tile Types.
Photoshop Express is a smart phone app and created to accept any image regardless - not for serious editing surely!

(edit)
NB. .QU does have an excellent image editor with more features than in Raw refine (except ODR).
Finally, shoot in raw is the best solution 

Terry

I downloaded a sample dng and qimage was quite happy with it.
Guess I need to get a real camera sometime.
Thanks for the help.

Apparently LR just puts a DNG wrapper around the jpeg. Apparently to reduce the number of file types.
Not very useful.

Never Iphone.