The Extended CPU Mode configuration bit is enabled but the program was not built using extended CPU instructions.
MPLAB® X IDE displays this message when the extended instruction set bit is set on a PIC18 device but the selected compiler doesn't support the extended instructions or has not been configured to use them. The MPLAB® XC8 compiler does not support the extended instruction set because it generates smaller code using the non-extended instruction set than it would, using the extended instructions. Some third-party compilers also may not support the extended instruction set.