On WinNT4(SP6a), the following script works in both cgi and isapi mode with the default php.ini, which has session auto_start turned off:

<?php
session_start();
session_register("cntr");
$cntr++;
echo "Counter is: $cntr";
?>

If I turn on session auto_start in php.ini with:

  session.auto_start = 1

all is well in cgi mode, but isapi mode generates the following error:

Counter is: 1
Warning: open(/tmp\sess_20b9e255f10a4bde02c3f9fe0d5d6779, O_RDWR) failed: m (2) in Unknown on line 0
Warning: Failed to write session data (files). Please verify that the current setting of session.save_path is correct (/tmp) in Unknown on line 0

The /tmp directory exists, is world read/writeable and is working fine in all modes without session.auto_start and in cgi mode with auto_start.

Changing session.save_path to '\tmp' (from '/tmp') makes no difference.

PHP is 4.0.4, build date 12/20/2000

Thanks.