I received multiple reports that after latest Kindle Fire update MOBI files created by KCC don't work anymore.
It is hard for me to debug that as I don't have access to any Fire tablet. Additionally everything work correctly in Kindle Previewer even in Fire mode.
http://www.amazon.com/forum/kindle?_...x1SWENKY1PWNJ9
Considering that factory reset fixing this issue for few days it look like major bug in official reader app.