WIX Installing App in new VirtDir links twice to new AppPool - iis

Question

Am trying to create a new WebApp, OPCClientWS, under an existing VirtDir, indx, under the root of the Default Web Site. The path will be /indx/OPCClientWS. This path actually does get created and is linked to a newly-created App Pool.
However, in the App Pool, I end up with an extra App reference: //indx/OPCClientWS. With this additional App reference in place, IIS will not start the website at all, throwing error 80070057:
The World Wide Web Publishing Service (WWW Service) did not register
the URL prefix http://*:80//indx/OPCClientWS for site 1. The URL may
be invalid. The site has been disabled. The data field contains the
error number.
Salient parts of the wxs code are as follows:
<Feature Id="ProductFeature" Title="OPCClientWS" Level="1">
<ComponentGroupRef Id="ProductComponents" />
<ComponentRef Id="AnSM_AppPoolInstall"/>
<ComponentRef Id="AnSM_WebDir"/>
</Feature>
Locating the root of the existing website, which already contains the indx Virtual Directory:
<Fragment>
<iis:WebSite Id="localhost_root" Description="Default Web Site">
<iis:WebAddress Id="localhost_addr" IP="AllUnassigned" Port="80"/>
</iis:WebSite>
</Fragment>
Creating the App Pool for the Application, set up in the next Fragment:
<Fragment>
<DirectoryRef Id="INSTALLFOLDER">
<Component Id="AnSM_AppPoolInstall" Guid="{8C762E41-A06F-49F9-8846-29CB148A446B}" KeyPath="yes">
<iis:WebAppPool Id="AnSM_AppPool" Name="AnSMAppPool" ManagedRuntimeVersion="v2.0" Identity="networkService"/>
</Component>
</DirectoryRef>
</Fragment>
Adding the WebVirtualDirectory to the existing Website:
<Fragment>
<DirectoryRef Id="INSTALLFOLDER">
<Component Id="AnSM_WebDir" Guid="{42A87FEB-BF0A-430D-8F23-3C4F8FE4E85F}" KeyPath="yes">
<CreateFolder/>
<iis:WebVirtualDir Id="OPCClient_VirtDir" Alias="indx/OPCClientWS" Directory="INSTALLFOLDER" WebSite="localhost_root">
<iis:WebApplication Id="AnSM_OPCWS" Name="OpcClientWS" WebAppPool="AnSM_AppPool"/>
<iis:WebDirProperties Id="AnSM_WebProps" AnonymousAccess="no" BasicAuthentication="no" WindowsAuthentication="yes"/>
</iis:WebVirtualDir>
</Component>
</DirectoryRef>
</Fragment>
And installing the various components into the directory (in Program Files), pointed to by the Virtual Directory:
<Fragment>
<Directory Id="TARGETDIR" Name="SourceDir">
<Directory Id="ProgramFilesFolder">
<Directory Id="XHQAnSM" Name="Siemens AnSM">
<Directory Id="INSTALLFOLDER" Name="OPCClientWS">
<Directory Id="OPCClientWS.Content"/>
<Directory Id="OPCClientWS.Binaries" Name="bin"/>
<Directory Id="OPCClientWS.Symbols" Name="bin"/>
</Directory>
</Directory>
</Directory>
</Directory>
</Fragment>
Target platform is Windows 2008R2 64-bit, IIS 7.5 I have searched the web ad nauseum. Is there a way to debug what is being sent to IIS (e.g., using appcmd or similar)?
FWIW, I would submit this to wixtoolset, but their bug submission website seems to be hosed...

Answer 1

Digging into the applicationHost.config file (at C:\Windows\System32\inetsrv\config), I found that there was a stuck application, probably due to a previous failed installation. I suspect this might have been caused by a leading slash in the Alias of the iis:WebVirtualDir element.
Offending lines are:
<application path="//indx/OPCClientWS" applicationPool="AnSMAppPool">
<virtualDirectory path="/" physicalPath="C:\Program Files (x86)\Siemens AnSM\OPCClientWS" />
</application>
Shutting down IIS, removing the lines, and restarting fixed the problem.