Flash a .hex to an ATtiny45 with Arduino
Googling the error gives this tutorial. Towards the bottom of the page they say 


  You’ll probably get the following message, but don’t worry, the upload should have worked anyway:
  
  avrdude: please define PAGEL and BS2 signals in the configuration file for part ATtiny85


So it seems this can be ignored and the part has been programmed!