I tried your code with memcpy and for me it works. Try this:
Code:
#include <acknex.h>
#include <default.c>

void main ()
{
	wait(1);
	byte bytez[4];
	float f = 852140;
	var fa = f;
	memcpy( bytez, &f, sizeof(f) );
	var x;
	int i;
	for(i=0;i<4;i++)
	{
		x = bytez[i];
		error(str_for_num(0,x));
	}
}


I get 192,10,80,73.

When displaying your bytes in a digits panel, note that digits only accept vars. So you should always use vars to set their value to the value of your byte and then display the vars.