Sorry to be late.
I have no problem using K4PC 1.7.1 with my latest MobiHandler. I set up a new Windows installation, downloaded and installed K4PC 1.7.1, and examined what it installed. I found no significant changes from K4PC 1.5.0. I see no reason K4PC 1.7.1 is incompatible with MobiHandler...
I recommend the following steps to try the following steps.
- Uninstall the MobiHandler.
- Install K4PC again (you don't need to uninstall K4PC.)
- (Adjust the default application for *.azw/*.mobi manually, if you prefer to do so).
- Install the MobiHandler.
And please wait for a while to start the above steps. I'm soon (within hours) uploading the latest version (1.1.1271)...