I have reinstated my sample code at http://www.tonymarston.co.uk/error.zip

There are instructions inside on how to reproduce the error.

This bug looks to be the same as bug 26286: http://bugs.php.net/bug.php?id=26286

The original problem here, reproduced using the script bundle posted by Tony, triggers crashes in free() when run with "MALLOC_CHECK_=3", using 5.0.4-dev.  Backtrace below.  Doesn't look like this is Apache-related:

#5  0x0041baca in free () from /lib/tls/libc.so.6
No symbol table info available.
#6  0x010035b7 in _efree (ptr=0x86e443c) at /net/jedi/local/php/5.0/Zend/zend_alloc.c:287
        p = (zend_mem_header *) 0x4e0800
        cache_index = 6
#7  0x0101f1fa in zend_hash_destroy (ht=0x86f1714)
    at /net/jedi/local/php/5.0/Zend/zend_hash.c:526
        p = (Bucket *) 0x0
        q = (Bucket *) 0x86e47dc
#8  0x01029c7f in zend_objects_free_object_storage (object=0x872be84)
    at /net/jedi/local/php/5.0/Zend/zend_objects.c:91
No locals.
#9  0x0102c24a in zend_objects_store_del_ref (zobject=0x0)
    at /net/jedi/local/php/5.0/Zend/zend_objects_API.c:159
        handle = 1
        obj = (struct _store_object *) 0x86d9b88
#10 0x010170d0 in _zval_dtor (zvalue=0x86efb2c)
    at /net/jedi/local/php/5.0/Zend/zend_variables.c:61
No locals.
#11 0x0100c491 in _zval_ptr_dtor (zval_ptr=0x10a995c)
    at /net/jedi/local/php/5.0/Zend/zend_execute_API.c:392
No locals.
#12 0x0104b894 in zend_do_fcall_common_helper (execute_data=0xbff34610,
    opline=0x86ee780, op_array=0x86e306c)
    at /net/jedi/local/php/5.0/Zend/zend_execute.c:2797
        i = 141458196
        p = (zval **) 0x86efb2c
        arg_count = 17471360
        original_return_value = (zval **) 0xbff346ac
        current_scope = (zend_class_entry *) 0x0
        current_this = (zval *) 0x0
        return_value_used = 1
        should_change_scope = 1 '\001'
#13 0x0104ba48 in zend_do_fcall_by_name_handler (execute_data=0x0, opline=0x86ee780,
    op_array=0x86e306c) at /net/jedi/local/php/5.0/Zend/zend_execute.c:2825
No locals.
#14 0x01039b77 in execute (op_array=0x86e306c)
    at /net/jedi/local/php/5.0/Zend/zend_execute.c:1400
        execute_data = {opline = 0x86ee780, function_state = {
    function_symbol_table = 0x870e404, function = 0x872a444, reserved = {0x100f260,
      0x86e3364, 0xbff36970, 0x0}}, fbc = 0x872a444, fbc_constructor = 0x0,
  op_array = 0x86e306c, object = 0x86efb2c, Ts = 0xbff33430,
  original_in_execution = 0 '\0', calling_scope = 0x86f0a54, prev_execute_data = 0x0}
#15 0x01018b25 in zend_execute_scripts (type=8, retval=0x0, file_count=3)
    at /net/jedi/local/php/5.0/Zend/zend.c:1069
        files = 0xbff34764 ""
        i = 1
        file_handle = (zend_file_handle *) 0xbff36970
        orig_op_array = (zend_op_array *) 0x0
        local_retval = (zval *) 0x0

I have this loop:

for ($i = 0, $_i = count($items); $i < $_i; $i++) {
   $item_index[$items[$i]['item_id']] =& $items[$i];
}

I run it on two platforms:
WinXP - PHP 4.3.4 - Apache/2.0.48 (Win32)
Linux - PHP 4.3.10 - Apache/2.0.52 (Fedora)

On Linux - no problems.
On WinXP - once count($item_classes) > 107, the script dies

In addition to my yesterday's comment: I installed PHP 4.3.10 on the WinXP - no effect on the problem.

And pardon me if I'm too vague, but I'd like to mention that I remember having this problem a couple times before: once the data got large enough, my WinXP testing server stopped working, but Linux production server worked fine - hth.

Also, it seems that this might be an Apache bug: http://issues.apache.org/bugzilla/show_bug.cgi?id=12340

Please try using this CVS snapshot:

  http://snaps.php.net/php5-STABLE-latest.tar.gz
 
For Windows:
 
  http://snaps.php.net/win32/php5.0-win32-latest.zip

I have tried that snapshot and the problem has not re-appeared. It appears you have fixed it.

Good. Not reproducible -> closed.