RF24Network::setup_watchdog(unsigned char)

[Esaca]

hello guys, PLEASE HELP ME :(
when i compile my code there error wrote like this :

C:\Users\Esaca\AppData\Local\Temp\ccmOb4Nz.ltrans0.ltrans.o: In function `main':

ccmOb4Nz.ltrans0.o:(.text.startup+0x53e): undefined reference to `RF24Network::setup_watchdog(unsigned char)'

ccmOb4Nz.ltrans0.o:(.text.startup+0xa0e): undefined reference to `RF24Network::sleepNode(unsigned int, int)'

collect2.exe: error: ld returned 1 exit status

exit status 1
Error compiling for board Arduino/Genuino Uno.

what should i do???