I haven't gone through the code completely, but taking another quick look at the schematic I noticed there aren't any pull-ups used for the buttons. I did see a TRISB=%11111111 in there, as well as checking one of the buttons low as a condtion in an IF...THEN statement used to enter the SetupEntryLoop (I am assuming the logic is the same on all three). So they are floating, and should be pulled-up. You could just use those 10K pull-ups you removed from the SCL/SDA lines (which should now have 4.7K) and add them to the pins for each of the buttons. Just need one additional for the third button.

Steve