I don't know if this is the best solution but it works for me.
In "GQview Tools"->Edit->Preferences->Editors change the command from "gimp-remote -n %f" to "/usr/bin/gimp-2.6 -n %f".
It may be more robust, in the case of upgrading Gimp, to use /usr/bin/gimp rather than /usr/bin/gimp-2.6 (/usr/bin/gimp is a symlink to /usr/bin/gimp-2.6) but I am happy to take on the extra task when Gimp is upgraded for the benefit of making the action more direct.
Similarly, it may be more robust to use gimp-2.6 rather than /usr/bin/gimp-2.6 in case it is is ever moved from /usr/bin, but again I am happy to fix when needs must for the benefit of making the action more direct.
Any thoughts about why GQview is configured to use gimp-remote rather than gimp?