there are no errors in the IIS7 event log only "information" logs informing me its not really being used
"A worker process with process id of '2636' serving application pool 'Webmail' was shutdown due to inactivity. Application Pool timeout configuration was set to 20 minutes. A new worker process will be started when needed."
this is the 500 error
500 - Internal server error.
There is a problem with the resource you are looking for, and it cannot be displayed.
when i refreshed the error page it loaded the message without the attachment and allowed me to forward the message, i did receive it but still no attachment
apparently it was a php error not an IIS error, but that gave me the idea to dig into the error itself a bit... here is the php error
PHP Warning: fopen(): Filename cannot be empty in C:\inetpub\wwwroot\Webmail\plugins\filesystem_attachments\filesystem_attachments.php on line 84
this is the iis call before the error
2011-12-21 21:12:40 ::1 GET / _task=mail&_id=9899985094ef24bc6f0394&_action=compose 80 - ::1 Mozilla/5.0+(Windows+NT+6.0;+WOW64;+rv:7.0.1)+Gecko/20100101+Firefox/7.0.1 500 0 0 1077