You may see this error in the MegaWizard message window in Quartus® II 12.0SP2 when generating Altera® UniPHY external memory interface IP with clock definitions which result in non integer values of clock period in ps. The memory IP performs the following check:
set period_ps [expr10^6/]
if ([expr int(*2)] == [expr int()*2])
If this is not true then the error will be reported in the MegaWizard message window. For example where a 375MHz clock is used, int(*2) is 5333ps but int()*2 is 5334ps.