See section 10.3 Portc, Trisc and Latc registers of data sheet.
"Note: On a Power-on Reset, these pins, except RC4 and RC5, are configured as digital inputs. To use pins RC4 and RC5 as
digital inputs, the USB module must be disabled (UCON<3> = 0) and the on-chip USB transceiver must be disabled (UCFG<3> = 1)."