Installing a module with appcmd causes http error 503

If I install a module  (e.g. Isapi, IsapiFilter, WebSocket) via the inetmgr UI, it properly adds the dll to the inetsrv folder (e.g. If I enable Isapi, isapi.dll will be installed in inetsrv folder). However, if I try to install a module with appcmd, the dll is not properly installed, so IIS always returns error 503

   > appcmd install module /name:IsapiModule /image:"c:\Windows\System32\inetsrv\isapi.dll" /add:true

   > appcmd install module /name:IsapiFilterModule /image:"c:\Windows\System32\inetsrv\filter.dll" /add:true

I've seen this on IIS 7.5 and 8.

How can I reproduce the steps that the UI takes using appcmd? I would like to automate the process.