Accessing Biztalk HTTP .dll returns 500

Any hints or tips you have for this C++ programmer in a mire of IIS and
networking are very much appreciated :D

I can't debug why I am getting 500's when trying to access, through a
virtual directory using Internet Explorer, C:\Program Files\Microsoft
BizTalk Server 2004\HttpReceive\BTSHTTPReceive.dll.  According to the
MSDN link below I should be getting a blank page, with entries in the
Event Viewer for Biztalk.

I have previously had days of hassle with 403's and 401's trying to get
this working.  For the 500 I get no errors in the Event Viewer. The IIS
log reveals nothing to me, it reads (using an existing virtual
directory, then one I created) :

2006-10-24 04:09:25 W3SVC1 MyServer 127.0.0.1 GET
/hwsmessages/BTSHTTPReceive.dll
|440|ASP_0116|Missing_close_of_script_delimiter 80 - 127.0.0.1 HTTP/1.1
Mozilla/4.0+(compatible;+MSIE+6.0;+Windows+NT+5.2;+.NET+CLR+1.1.4322)
ASP.NET_SessionId=ytnfuq45fyyweu55jgg1dziz - localhost 500 0 0 615 377
15

2006-10-24 04:09:35 W3SVC1 MyServer 127.0.0.1 GET
/newhttprec/BTSHTTPReceive.dll
|440|ASP_0116|Missing_close_of_script_delimiter 80 - 127.0.0.1 HTTP/1.1
Mozilla/4.0+(compatible;+MSIE+6.0;+Windows+NT+5.2;+.NET+CLR+1.1.4322)
ASP.NET_SessionId=ytnfuq45fyyweu55jgg1dziz - localhost 500 0 0 614 376
15


Following instructions from...
ms-help://BTS_2004/SDK/htm/ebiz_sdk_samples_yzhk.htm
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/BTS_2004WP/html/ffda72df-5aec-4a1b-b97a-ac98635e81dc.asp
  ( Setting Up HTTP Receive)
and general googling I have triple checked that
- Administrator is a member of all the Biztalk and Internet related
groups
- The IIS Application Pool Identity, Web Sites' Anonymous Access and in
Windows Component Services the IIS COM+ services all use the
Administrator ID.
- IIS has Web Services extensions allowing access to that .dll.  I
additionally allowed access to everything.
- All related NTFS permissions seem fine
- In the Local Policies I have enabled Success and Failure auditing for
both Logon options.

I think I tried everything except resetting the server and
throwing it out the window.

Thanks in advance :)