for info - if anyone else is struggling with this bit...
IIS will deny access to bin fodlers
You can get around it by commenting out the bin section of the hiddensegments section of the $windir\System32\inetsrv\configapplicatonhost.config:
<hiddenSegments applyToWebDAV="true">
<add segment="web.config" />
<!--<add segment="bin" />-->
<add segment="App_code" />
<add segment="App_GlobalResources" />
<add segment="App_LocalResources" />
<add segment="App_WebReferences" />
<add segment="App_Data" />
<add segment="App_Browsers" />
</hiddenSegments>