Chankast doesn't work with disc images directly (so stop trying to associate them with Chankast or double-clicking them- the leads you nowhere). You need to use virtual drive software like Daemon Tools and mount the game image with it; thenyou can use it in Chankast.
Then again, nothing should prevent you from trying other [far better] emulators like Demul or nullDC, as those can work with disc images as is (still, don't go trying to associate disc images with those applications or trying to double-click the images because that's not how you go about things).