doesn't work for me, when activating the admin in theme option.
if i comment out the include line in mainfile php, everything works fine.

the _exactly_ same setup works perfectly fine on apache(rest is all the same).

if seems that it allways fails the
if( ! defined( 'XOOPS_CPFUNC_LOADED' ) )
condition

commenting it out fails on:
@list( , $tmp_s ) = explode( "<div class='content'>" , $tmp_s , 2 ) ;
and then on
list( $tmp_s , $tmp_after ) = explode( "<td width='1%' background='".XOOPS_URL."/modules/system/images/bg_content.gif'>" , $tmp_s ) ;


any ideas?

it seems that the function registered with register_shutdown_function
never gets called (or when the connection is already closed)

bug in IIS? bug in PHP? bug in XOOPS?

I don't know, sorry.

Anyway, this must be not an issue of XOOPS or XOOPS's module.
A problem of lower level. (IIS or PHP)