CLOCK_50 was determined to be clock but was found without an associated clock assign.

Have you made a constraints (.sdc) file? If not you will need to in order to tell Quartus what clocks you have and at what frequency.

set_time_format -unit ns -decimal_places 3
# ##############################################################################  Create Input reference clocks
create_clock -name {CLOCK_50} -period 20.000 -waveform { 0.000 10.000 } 
# ##############################################################################  Now that we have created the custom clocks which will be base clocks,#  derive_pll_clock is used to calculate all remaining clocks for PLLs
derive_pll_clocks -create_base_clocks
derive_clock_uncertainty