package fifo1;

class genfra;
rand bit [31:0] dword1;
rand bit [31:0] dword2;
endclass :genfra


class crefra;

local genfra fifoc[$] ;
genfra temp1 ;
integer success,i,dly;

function new(ref genfra fifo[$]);
fifoc = fifo;
endfunction

task gennpush();
     for(i = 0 ; i < 20 ;i++)
       begin
       temp1=new();
       success = temp1.randomize();
       success = randomize(dly) with {dly > 2;dly < 5;};
       $display("time=%d.. temp1.dword1 = %08x  ",$time,temp1.dword1);
       $display("time=%d.. temp1.dword2 = %08x  ",$time,temp1.dword2);
       fifoc.push_back(temp1);
       #dly;
       end
endtask

endclass

class prifra;
local genfra fifop[$] ;

function new(ref genfra fifo[$]);
fifop = fifo;
endfunction

task popnprint();
genfra temp2 ;
       forever
       begin
           $display("time=%d..before pop ",$time);
           if(fifop.size())
           begin
           #5;
           $display("fifo size before pop ",fifop.size());
           temp2=fifop.pop_front();
           $display("time=%d.. temp2.dword1 = %08x  ",$time,temp2.dword1);
           $display("time=%d.. temp2.dword2 = %08x  ",$time,temp2.dword2);
           $display("fifo size after pop ",fifop.size());
           end
           else
            #1;
       end
endtask
endclass

endpackage



module top;
timeunit 1ns;
int success,i;
import fifo1::*;
genfra fifo[$] ;
crefra cf = new(fifo);
prifra pf = new(fifo);


initial
 begin
  fork
    cf.gennpush();
    pf.popnprint();
  join any
       $finish;
 end


final $display("time=%d Ending Simulation ",$time,);

endmodule

log file : 

ncverilog: 05.83-p002: (c) Copyright 1995-2006 Cadence Design Systems, Inc.
TOOL:   ncverilog   05.83-p002: Started on Dec 14, 2006 at 19:44:23 IST
ncverilog
    -l
    ./transcript.clachan.log
    +ncaccess+rw
    +notimingchecks
    +libext+.v
    +sv
    +svseed=35
    clachan.sv
file: clachan.sv
fifoc = fifo;
    |
ncvlog: *E,WOUPYR (clachan.sv,21|4): As a temporary implementation restriction, an array class member reference is not permitted in this context.
fifoc = fifo;
           |
ncvlog: *E,WOUPSR (clachan.sv,21|11): A reference to an entire array is not permitted in this context [SystemVerilog].
fifop = fifo;
    |
ncvlog: *E,WOUPYR (clachan.sv,43|4): As a temporary implementation restriction, an array class member reference is not permitted in this context.
fifop = fifo;
           |
ncvlog: *E,WOUPSR (clachan.sv,43|11): A reference to an entire array is not permitted in this context [SystemVerilog].
    package worklib.fifo1:sv
        errors: 4, warnings: 0
import fifo1::*;
           |
ncvlog: *E,NOPBIND (clachan.sv,73|11): Package fifo1 could not be bound.
genfra fifo[$] ;
     |
ncvlog: *E,SVNOTY (clachan.sv,74|5): Syntactically this identifier appears to begin a datatype but it does not refer to a visible datatype in the current scope.
genfra fifo[$] ;
            |
ncvlog: *E,ILLPRI (clachan.sv,74|12): illegal expression primary [4.2(IEEE)].
genfra fifo[$] ;
               |
ncvlog: *E,EXPIDN (clachan.sv,74|15): expecting an identifier [3.2][3.8][3.9(IEEE)].
crefra cf = new(fifo);
          |
ncvlog: *E,EXPSMC (clachan.sv,75|10): expecting a semicolon (';') [12.3.2(IEEE)].
crefra cf = new(fifo);
                    |
ncvlog: *E,EXPSMC (clachan.sv,75|20): expecting a semicolon (';') [12.3.2(IEEE)].
prifra pf = new(fifo);
          |
ncvlog: *E,EXPSMC (clachan.sv,76|10): expecting a semicolon (';') [12.3.2(IEEE)].
prifra pf = new(fifo);
                    |
ncvlog: *E,EXPSMC (clachan.sv,76|20): expecting a semicolon (';') [12.3.2(IEEE)].
       $finish;
             |
ncvlog: *E,MISEXX (clachan.sv,85|13): expecting an '=' or '<=' sign in an assignment [9.2(IEEE)].
    module worklib.top:sv
        errors: 9, warnings: 0
ncvlog: *F,NOTOPL: no top-level unit found, must have recursive instances.
ncverilog: *E,VLGERR: An error occurred during parsing.  Review the log file for errors with the code *E and fix those identified problems to proceed.  Exiting with code (status 2).
TOOL:   ncverilog   05.83-p002: Exiting on Dec 14, 2006 at 19:44:23 IST  (total: 00:00:00)

I used a mailbox to do what you want. Although mailboxes aren't formally supported in IUS, I included a mailbox class that works the same way (all files attached).

Here's the main change to your code:

package fifo1;

import mailbox::*;

class genfra extends mb_item;
  rand bit ⎫:0] dword1;
  rand bit ⎫:0] dword2;
endclass :genfra

class crefra;
  mailbox   fifoc ;
  genfra    temp1 ;
  int       dly;

  function new(mailbox fifo);
    fifoc = fifo;
  endfunction

  task gennpush();
    repeat (20) begin
      temp1=new();
      assert(temp1.randomize());
      assert(randomize(dly) with {dly > 2;dly < 5;});
      $display("time=%d.. temp1.dword1 = %08x  ",$time,temp1.dword1);
      $display("time=%d.. temp1.dword2 = %08x  ",$time,temp1.dword2);
      fifoc.put(temp1);
      #dly;
    end
  endtask
...
endpackage

module top;
  timeunit 1ns;
  import fifo1::*;
  import mailbox::*;

  mailbox fifo = new(10);
  crefra cf = new(fifo);
  prifra pf = new(fifo);
...
endmodule