It seems that DPP4 cannot open (i.e., import/input) some .tif type files.  The specific files that are affecting me were created by GIMP 2.10.4 and are uncompressed .tif type (both 8 bit and 16bit) files.  The related scenario involves the case where initial processing of a raw file (type .CR2) was done by DPP4.  Then a 16bit .tif is created by DPP4 which is then used as input to GIMP.  After some additional editing another .tif type file (either 16bit or 8bit) is exported from GIMP.  The later cannot be imported by DPP4.

No other image processor that I'm using has any problem opening these files.  This includes GIMP, Rawtherappee, XnViewMP, Picasa, Windows Photo Viewer, MS Paint and interestingly Canon's My Image Garden.