Mine works fine..

#!/usr/bin/perl -w
use strict;

my $self = {};
$self->{data} = './biglog.log';
$self->{process} = 1;
my $increment = 1000000;

#For this example $$config{blocksize} == 550
#

my $blocksize = 550;
my $startblock = 1;

    my $records = int($increment / $blocksize);
    my $bytecnt = $blocksize * $records;
    
    #After caluclations this prints out as 999900
    print "bytecnt[$bytecnt]\n";
    
    my $file = 0;
    
    open PARENT, $$self{data} or die "Cannot open [$$self{data}] for i
+ncremental parsing\n";
        
    while(1){
    
        $file++;
        my $data = "";
        
        if($file == 1){
            
            read(PARENT, $data, $startblock);
            read(PARENT, $data, $bytecnt);
                        
            open(FILE, ">tmp\\$$self{process}".sprintf("%02d", $file).
+".dat") 
                    or die "Cannot open tmp\\$$self{process}".sprintf(
+"%02d", $file).".dat for incremental writing\n";
            print FILE $data;
            close(FILE);
            
            next;
        }
        
        read(PARENT, $data, $bytecnt);
        
        open(FILE, ">tmp\\$$self{process}".sprintf("%02d", $file).".da
+t") 
            or die "Cannot open tmp\\$$self{process}".sprintf("%02d", 
+$file).".dat for incremental writing\n";
        print FILE $data;
        close(FILE);
        
        if(eof(PARENT)){    
            last;
        }
                
    }
    
    close(PARENT);
    die;
[download]

I get

-rw-r--r-- 1 loot poot 6056869 May 30 10:48 biglog.log
-rw-r--r-- 1 loot poot    1425 May 30 10:51 incspl.pl
-rw-r--r-- 1 loot poot  999900 May 30 10:52 tmp\101.dat
-rw-r--r-- 1 loot poot  999900 May 30 10:52 tmp\102.dat
-rw-r--r-- 1 loot poot  999900 May 30 10:52 tmp\103.dat
-rw-r--r-- 1 loot poot  999900 May 30 10:52 tmp\104.dat
-rw-r--r-- 1 loot poot  999900 May 30 10:52 tmp\105.dat
-rw-r--r-- 1 loot poot  999900 May 30 10:52 tmp\106.dat
-rw-r--r-- 1 loot poot   57468 May 30 10:52 tmp\107.dat

Your problem must be the config??.. (Oh no.. could it be because you're using windoz some funny filesystem- like.. ?!?!)